OBD-II Code P1625: Comprehensive Guide to Engine & Module Power Supply Malfunctions

What Does P1625 Mean?

P1625 is a manufacturer-specific code indicating the Powertrain Control Module (PCM) or Engine Control Module (ECM) unexpectedly lost its primary electrical power. The PCM is the operational brain of your vehicle. When it suddenly loses power and reboots, it stores this code to flag a critical electrical problem.

Technical definition: The most common generic meaning is 'PCM/ECM System Reset' or 'B+ Supply to Control Module Malfunction'. This signifies the PCM detected an unplanned loss of its main power supply or a reboot of its internal processor. However, for many manufacturers, this code points to entirely different systems, such as the immobilizer, cooling fans, or data bus communication. You must verify the specific definition for your vehicle.

Can I Drive With P1625?

No — Do Not Drive. When P1625 indicates a PCM power supply failure, driving is unsafe. The engine stalls without warning at any speed, creating a severe accident risk and disabling power steering. Repeated low voltage events also damage other electronic modules. If the code relates to a subsystem like the cooling fan (common on Ford or Hyundai), short-distance driving is possible, but you risk catastrophic engine overheating.

Common Causes

• Weak or Failing Battery (Very Common) — A battery failing to provide stable voltage is the leading cause. During engine cranking, if voltage drops below the PCM's operational threshold (typically 9.6 volts), the module shuts down and resets, logging a P1625.
• Loose or Corroded Battery Terminals and Grounds (Very Common) — A poor connection at the battery posts or where the main negative cable grounds to the chassis interrupts power to the entire vehicle, starving the PCM.
• Faulty PCM Power Relay (Common) — The PCM receives power via a main relay. This relay fails internally, suffers burnt contacts, or sticks, causing intermittent or total power loss to the computer.
• Failing Alternator (Common) — A bad alternator failing to recharge the battery leads to a gradual decline in system voltage, eventually causing the battery to become too weak to keep the PCM powered.
• Faulty Ignition Switch (Common) — The ignition switch sends the 'wake-up' signal to the PCM relay. A worn-out switch intermittently cuts this signal, causing the PCM to shut down on bumpy roads.
• Blown PCM/Immobilizer Fuse (Less Common) — A dedicated fuse for the PCM or immobilizer system blows due to a short circuit or voltage spike, cutting off power. On Suzukis, this is the primary cause for an immobilizer-related P1625.
• Improperly Installed Aftermarket Accessories (Less Common) — Incorrectly wired remote starters, alarms, or stereo systems interfere with the PCM's power supply or create a significant parasitic draw that drains the battery.
• Voltage Spike from Improper Jump Start (Rare) — Connecting jumper cables with reverse polarity sends a voltage surge through the electrical system, damaging the PCM or triggering a hard reset.
• Damaged Wiring Harness (Rare) — Power or ground wires to the PCM chafe, break, or short out from vibration, heat, or rodent damage.
• Internal ECU Logic Error (Rare) — On European makes like Citroën, a severe voltage drop during startup triggers an internal 'software redundancy error' within the ECU, logging P1625 even if the main power circuit is intact.
• Failing Powertrain Control Module (PCM) (Very Rare) — An internal failure within the PCM itself causes it to reset. Consider this only after exhaustively testing all power, ground, and wiring possibilities.

Symptoms

• Engine Cranks But Fails to Start — The engine turns over, but the PCM lacks power to control fuel and spark. This is the most common symptom.
🎬 Watch: A guide to diagnosing the most common crank-no-start causes.
• Engine Stalls Intermittently While Driving — The vehicle runs fine and then suddenly shuts off when the PCM or its relay loses power. This is an extremely dangerous symptom.
• Engine Starts and Immediately Stalls — A classic symptom on vehicles where P1625 relates to the immobilizer (VW or Suzuki). The engine fires for 1-2 seconds and shuts off as the anti-theft system cuts fuel.
• Loss of Radio Presets, Clock, and Trip Meter — A significant power interruption triggering a P1625 is severe enough to reset the memory for other accessories in the vehicle.
• Flashing Immobilizer or Security Light — On makes like VW, Audi, and Suzuki, a blinking key or security light on the dashboard indicates a failure to recognize the key.
• Check Engine Light On (also visible on scanner) — The Malfunction Indicator Lamp (MIL) illuminates as soon as the PCM reboots and detects the improper shutdown.
• Reduced Power or 'Limp Mode' (also visible on scanner) — If the PCM experiences intermittent power faults, it enters a self-preservation mode limiting engine speed and power.
• Loss of Communication with Scan Tool (scan-tool only — no driver-felt sign) — If the PCM lacks power, a standard OBD-II scanner cannot communicate with it.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Replace Battery — Parts: $150-$300, Labor: $0-$100, ~0.6 hr book time (DIY)
• Clean or Replace Battery Terminals and Ground Straps — Parts: $5-$30, Labor: $50-$150, ~0.8 hr book time (DIY)
• Replace PCM Power Relay — Parts: $20-$70, Labor: $0-$75, ~0.2 hr book time (DIY)
  : OEM (Alt: {"brand": "Standard Motor Products", "part_number": "RY612"}, {"brand": "ACDelco", "part_number": "D1786C"})
  : OEM (Alt: {"brand": "Denso", "part_number": "567-0002"}, {"brand": "Bosch", "part_number": "0986AH0250"})
• Replace Blown Fuse — Parts: $1-$10, Labor: $0-$100, ~0.3 hr book time (DIY)
• Replace Alternator — Parts: $200-$500, Labor: $150-$400, ~2 hr book time (Intermediate)
  : OEM (Alt: {"brand": "Bosch (Reman)", "part_number": "AL8782X", "price_comparison": "$250-$350"}, {"brand": "DB Electrical", "part_number": "400-24193", "price_comparison": "$150-$200"})
  : OEM (Alt: {"brand": "Bosch (Reman)", "part_number": "AL1310X / AL6400X", "price_comparison": "$280-$320"})
• Replace Ignition Switch — Parts: $50-$300, Labor: $150-$400, ~2.5 hr book time (Intermediate)
  : OEM (Alt: {"brand": "Febi", "part_number": "W0133-1961488", "price_comparison": "$115+"})
• Repair Wiring Harness — Parts: $10-$50, Labor: $200-$800, ~5 hr book time (Professional)
• Replace Powertrain Control Module (PCM) — Parts: $600-$2000, Labor: $150-$400, ~1.5 hr book time (Professional)

DIY vs Professional

• Replace Battery — Beginner: Yes
  Tools: Wrench set, terminal cleaner brush, safety glasses, gloves. A memory saver preserves radio presets.
• Replace PCM Power Relay — Beginner: Yes
  Tools: None, or a small pair of pliers to pull the relay.
• Replace Alternator — Beginner: No
  Tools: Socket/wrench set, serpentine belt tool or breaker bar, pry bar, safety glasses, gloves.
• Replace Ignition Switch — Beginner: No
  Tools: Screwdriver set, trim removal tools, socket set, multimeter, vehicle-specific repair manual.

Used vs. New Parts: Buying Guide

When a used part is worth it: For an expensive component like an alternator, a used OEM part from a low-mileage donor vehicle is a cost-effective option for an older vehicle. It is often more reliable than a cheap aftermarket part.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Verify the donor vehicle was not scrapped due to electrical or engine failure.
• Ask the seller if the part has been tested.
• Match the part number exactly.

Decision logic:

• If The vehicle is newer or you plan to keep it long-term → Buy a new or remanufactured alternator from a reputable brand. The longer lifespan and warranty justify the cost.
• If The vehicle is older and budget is the primary concern → A used OEM or a quality remanufactured alternator is an acceptable choice. Avoid 'rebuilt' parts.
• If The part is for a critical service vehicle (ambulance, etc.) → Always buy new OEM to ensure maximum reliability.

Warranty tradeoff: Used parts typically come with a 30-90 day warranty. Remanufactured parts often have a 1-year to limited lifetime warranty. New OEM parts carry the manufacturer's standard parts warranty.

Worst-case if a used part fails: $300-$600 if a used part fails prematurely, requiring repeat labor costs plus the price of another replacement part.

What Happens If You Wait — Timeline

1. 0-2 weeks (intermittent): Code is set, MIL is on. You experience an occasional, unexplained no-start or a single stall, often only on cold mornings. (MPG impact: 0-5%% · Added cost: $0-$50 in wasted fuel and potential towing if stranded.)
2. 2 weeks - 3 months (frequent): Stalling or no-start events become frequent. Constant low-voltage events put significant stress on the starter motor and battery, accelerating their failure. (MPG impact: 5-10%% · Added cost: $250-$700 (Premature failure of the battery and/or starter motor).)
3. 3-6 months (systemic risk): A faulty alternator fails completely, leaving you stranded. If the code is for a cooling fan circuit (Ford/Hyundai), the engine overheats, leading to catastrophic damage. (MPG impact: 10-25%% · Added cost: $2,000-$5,000+ (Cost to repair a warped cylinder head due to overheating).)
4. 6+ months (safety hazard): The vehicle is completely unreliable. The risk of the engine stalling at high speed or in a busy intersection becomes dangerously high. (MPG impact: N/A% · Added cost: Potentially thousands in accident-related damages.)

Cost of Not Fixing It

• Immediate: High risk of engine stalling at any time, including in traffic or at highway speeds, leading to a serious accident. The vehicle also fails to start, leaving you stranded. (Added cost: Towing costs ($100-$300))
• 1-3 months: Repeated low-voltage events and hard resets put stress on the starter motor and sensitive electronics. Frequent stalling causes premature wear on the starter and battery. (Added cost: $200-$600 (Starter or Battery Replacement))
• 3+ months: If the code relates to a cooling fan malfunction (Ford/Hyundai), ignoring it leads to engine overheating, causing catastrophic damage like a warped cylinder head. (Added cost: $2000-$5000+)

Diagnosis Steps

1. Verify Code Definition and Check Freeze Frame Data
   Use an OBD-II scanner to confirm the exact definition of P1625 for your vehicle's make and year. Analyze the freeze frame data for P1625, which shows a snapshot of sensor values (like battery voltage) at the moment the fault occurred.
   Tools: Advanced OBD-II Scanner (Beginner)
2. Test Battery Health and Cranking Voltage
   Check the battery voltage with the engine off; a healthy battery reads ~12.6V. Have a helper crank the engine while you observe the voltage. It must not drop below 9.6 volts. A drop below this threshold confirms a weak battery is causing the PCM to reset.
   Tools: Digital Multimeter (Beginner)
3. Perform a Thorough Battery and Connection Inspection
   Visually inspect the battery terminals for white or blue-green corrosion. Ensure the terminal clamps cannot be twisted by hand. Follow the main negative cable to its connection points on the chassis and engine block; ensure they are clean, rust-free, and securely fastened.
   Tools: Wrench set, Wire brush, Safety glasses (Beginner)
4. Inspect PCM/Main Relay and Fuses
   Locate the fuses labeled 'PCM', 'ECM', 'ECU', 'EFI', or 'IMMO'. Visually inspect and test them with a multimeter. Locate the PCM power relay. Swap it with an identical relay from a non-critical circuit (like the horn) to see if the problem resolves.
   Tools: Owner's manual, Fuse puller or pliers, Multimeter (Intermediate)
5. [PRO TIP] Perform a Voltage Drop Test
   Set your multimeter to a low DC Volts scale. Connect the red lead to the PCM's ground pin at the connector and the black lead to the negative battery terminal. With the key on, the reading must be less than 0.1 volts. A reading higher than 0.2V confirms a bad ground connection. Repeat for the power side.
   Tools: Multimeter with back-probes, Vehicle-specific wiring diagram (Advanced)
6. [PRO TIP] Conduct a Parasitic Draw Test
   Disconnect the negative battery terminal. Set your multimeter to the 10A DC Amps setting and connect it in series. With the car off and doors closed for 30 minutes, the draw must be under 50 milliamps (0.05A). If higher, pull fuses one by one until the draw drops to pinpoint the faulty circuit.
   Tools: Digital Multimeter with Amp clamp or 10A setting (Advanced)
7. Test the Ignition Switch
   Check for correct and stable voltage at the output wires of the ignition switch in the 'ON' and 'START' positions. A flickering voltage reading when wiggling the key confirms a worn-out switch.
   Tools: Multimeter, Vehicle-specific wiring diagram (Advanced)
8. Inspect PCM Wiring Harness and Connectors
   Visually trace the wiring harness leading to the PCM. Look for chafing, melting, or rodent damage. Disconnect the PCM connector and inspect for corroded or pushed-out pins. Perform a 'wiggle test' by gently moving the harness to see if you trigger the fault.
   Tools: Flashlight, Mirror, Vehicle-specific wiring diagram (Advanced)
9. [ADVANCED] Test Relay and Control Circuits
   With the relay removed, verify one control-side pin receives 12V+ with the key on, and the other has continuity to ground. Verify the load-side has a constant 12V+ supply on one pin and continuity to the PCM's power input on the other. A lack of voltage or ground points to an ignition switch or wiring problem.
   Tools: Multimeter, Vehicle-specific wiring diagram (Advanced)
10. [ADVANCED] Check Live Data PIDs for Clues
    Monitor live data PIDs related to module voltage. Normal charging system voltage is between 13.5V and 14.8V with the engine running. Deviations pinpoint a charging system fault.
    Tools: Advanced OBD-II Scanner (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• Module Voltage: < 9.6V (During engine cranking, indicating a weak battery or bad connection.)
• Engine RPM: 0 or fluctuating wildly (At the moment of an engine stall while driving.)
• Engine Status: Cranking or Stalled (The fault is most often logged during startup or an unexpected shutdown, not during steady driving.)
• Time Since Codes Cleared: Very low (Often occurs shortly after a battery disconnect or replacement, triggering the code on the first startup.)

Related Codes

• P0562 — Means 'System Voltage Low'. This code confirms the condition causing P1625. If you see both, the battery or charging system is the prime suspect.
• U0100 — Means 'Lost Communication With ECM/PCM'. This code sets in other modules when the PCM unexpectedly powers down, strongly supporting that the PCM itself shut down.
• P0685 — Means 'ECM/PCM Power Relay Control Circuit/Open'. This points directly at the PCM's main relay or its control circuit, helping pinpoint the relay as the source of the power loss.
• P0606 — Means 'ECM/PCM Processor Fault'. A sudden power loss and reboot (P1625) corrupts the PCM's internal self-check. Always fix the power supply issue first.
• P1570 — Means 'Engine Start Blocked by Immobilizer'. Common on VW/Audi, this appears alongside P1625 when there is an anti-theft system failure.

Climate & Environmental Factors

• Cold Weather: Cold temperatures slow the chemical reactions inside a lead-acid battery, reducing power output by up to 50%. Thick engine oil requires more power to crank the engine. A weak battery fails a cranking voltage test in the cold, causing the PCM to reset.
• High Humidity and Salt Air: Moisture accelerates corrosion on battery terminals, ground straps, and wiring connectors. This corrosion creates unwanted resistance, starving the PCM of stable voltage and triggering a P1625.

How to Talk to a Mechanic About This Code

Say this: "I have a P1625 code and I'd like to schedule a diagnostic. My research shows this is often a power supply issue, so please start by testing the battery, checking the main grounds for voltage drop, and inspecting the PCM power relay before looking at the PCM itself."

This signals you are an informed customer and directs the technician to perform a logical, step-by-step diagnosis, starting with the most common and cheapest fixes. It prevents them from immediately quoting an unnecessary PCM replacement.

Avoid saying:

• 'My car is stalling, just fix it.'
• 'My check engine light is on, can you just look at it?'
• 'I think I need a new computer.'

Questions to ask before authorizing the repair:

• What was the battery's cranking voltage during your load test?
• What was the voltage drop reading across the main power and ground cables?
• Can you provide the freeze-frame data stored with the P1625 code?
• If you recommend a PCM replacement, what specific tests did you perform to condemn it?
• What is the warranty on this repair, including both parts and labor?

Where to Take It: Dealer vs Independent vs Chain

• Dealer: Recommended only if the issue is confirmed to be a complex, brand-specific problem or requires PCM programming.
  Best for: Vehicles still under powertrain warranty., Complex manufacturer-specific variations of the code (VW/Audi data bus issues, Suzuki immobilizer faults)., Confirmed PCM failure requiring proprietary programming.
  Downsides: Significantly higher labor rates and parts costs., Defaults to replacing a whole assembly rather than performing a circuit-level repair. (Typical cost: +50% vs. baseline)
• Independent Shop: Best fit for most P1625 scenarios. A good independent technician excels at the fundamental electrical troubleshooting this code requires.
  Best for: Out-of-warranty vehicles where the code means 'PCM Power Loss'., Core electrical diagnostics like voltage drop tests, parasitic draw tests, and wiring repair., Owners looking for better value and flexible repair options.
  Downsides: Shop quality varies; look for ASE certification in electrical diagnostics., Lacks expensive, proprietary tools for PCM programming on all makes. (Typical cost: +0% vs. baseline)
• Chain Shop: Not recommended for diagnosing an unknown P1625 fault. The risk of misdiagnosis is high.
  Best for: Simple battery replacement if you have already confirmed the battery is the fault.
  Downsides: Technicians lack advanced electrical diagnostic skills needed for intermittent faults., High pressure to sell common parts without a complete diagnosis, missing the true cause. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost exceeds 50% of the car's private-party value, seriously consider selling or trading in the vehicle instead of repairing it.

• Car worth $4000, fix is $2200: Walk away. The repair cost is over 50% of the car's value.
• Car worth $12000, fix is $1200: Fix it. The repair cost is only 10% of the vehicle's value and is a sound investment.
• Car worth $3000, fix is $2500: Walk away. The repair cost is 83% of the car's value, making it a poor financial decision.

What Scan Tool You Need for This Code

Minimum: A scanner that reads and graphs live data, specifically 'Control Module Voltage', and displays freeze-frame data.

A basic $20 code reader only shows the P1625 code. It lacks critical evidence like module voltage at the moment the fault occurred (freeze-frame data) or live charging system voltage, leaving you guessing at the cause.

Budget: BlueDriver Pro (~$90) — Connects to your smartphone, reads manufacturer-specific definitions for P1625, displays freeze-frame data, and graphs live module voltage to spot drops.

Mid-range: XTOOL D7 (~$350) — Provides full system diagnostics and bidirectional control. This allows you to actively test components like the PCM power relay by commanding it on and off.

Professional: Autel MaxiCOM MK808 / MK900BT (~$500-800) — Offers full bidirectional controls, advanced ECU information, and guided diagnostics. If the final diagnosis is a failed PCM, these tools perform the necessary programming for the new module.

Rent vs buy: If this is a one-time diagnosis, auto parts stores loan capable scanners for free with a refundable deposit. Buy a scanner only if you plan to perform your own diagnostics regularly.

How to Clear the Code After You Fix It

1. Reconnect battery (if disconnected for repair).
2. Use an OBD-II scan tool to clear all diagnostic trouble codes (DTCs).
3. Perform a complete drive cycle to allow the vehicle's readiness monitors to run their self-tests.

Drive cycle (~30 minutes): Cold start (sit for 8+ hours). Idle for 2-3 minutes with electrical loads on (A/C, defroster). Drive for 10-15 minutes with mixed city (stop-and-go) and highway speeds (steady 55 mph for 5+ minutes). Allow the vehicle to cool down.

Readiness monitors affected: Catalyst (CAT) monitor, Evaporative (EVAP) System monitor, Oxygen (O2) Sensor monitor, Fuel System Monitor

Before emissions retest: drive at least 100 miles to fully set monitors.

Watch out for:

• Disconnecting the battery clears the code but resets all readiness monitors to 'Not Ready', causing an automatic emissions test failure.
• The code returns immediately if the underlying electrical problem (weak battery, bad ground, faulty relay) is not fixed.
• Monitors like EVAP and Catalyst require specific driving conditions (steady speed, fuel tank between 1/4 and 3/4 full) to run their tests.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An illuminated Check Engine Light results in an automatic failure. After repair, a full drive cycle must be completed to set all required readiness monitors to 'Ready' before a re-test.
• New York: A P1625 code and illuminated MIL cause an automatic failure. Clearing the code right before the test results in a 'Not Ready' status for monitors, also leading to failure.
• Texas: An active P1625 code fails the OBD portion of the inspection. For 2001 and newer vehicles, only one non-continuous monitor is allowed to be 'Not Ready'.

Most Commonly Affected Vehicles

• General Motors (Chevrolet, GMC, Cadillac) Various Trucks and SUVs (2000-2015) — Commonly 'B+ Supply to VCM System Problem'. Often caused by faulty ignition switches or poor grounds. A widespread recall for ignition switches (NHTSA Campaign 14V047000) causes similar symptoms.
• Acura / Honda Various (2000-2012) — Typically means 'PCM Unexpected Reset,' pointing directly to a power interruption. Failing main relays (PGM-FI relay) are a frequent culprit.
• Volkswagen / Audi Various (Golf, Jetta, A4) (2000-2016) — Frequently P1625 is 'Powertrain Data Bus: Implausible Message from TCU', indicating a communication problem between the engine and transmission controllers, or an immobilizer failure.
• Suzuki Swift, Grand Vitara, Dzire (2005-2017) — Almost always means 'Immobilizer Antenna Malfunction'. The cause is a blown fuse, a bad connection at the immobilizer module, or a faulty antenna ring.
• Ford Focus, Taurus, Windstar (1998-2007) — Frequently means 'B+ Supply To VCRM Fan Circuit Malfunction,' relating to the Variable Control Relay Module that controls the engine cooling fans, not a general PCM power loss.
• BMW Various (e.g., 3-Series, 5-Series) (2002-2012) — Indicates a fault in the power supply to the accelerator pedal position sensor, affecting throttle control.
• Hyundai / Kia Santa Fe, Sonata, Optima (2001-2010) — Points to a 'Cooling Fan Relay Circuit Malfunction,' indicating a problem in the fan control circuit. It is not a core PCM power failure.
• SAAB 9-5 (2002-2010) — Means 'No Bus data From TC/ABS', indicating a communication breakdown on the data bus between the engine module and the traction control/ABS module.

Manufacturer-Specific Notes

• General Motors / Acura / Generic: Indicates a power loss or unexpected reset of the main engine computer. Diagnosis starts with the battery, grounds, and main relay.
• Ford / Hyundai / Kia: Relates to the cooling fan control circuit, specifically the power supply to the fan control module or relay. The engine is not at immediate risk of stalling.
• Volkswagen / Audi: Indicates 'Powertrain Data Bus: Implausible Message from TCU', a communication error between the engine and transmission computers, or an immobilizer authorization failure.
• Suzuki / Maruti: Exclusively means 'Immobilizer Antenna Malfunction'. Check the immobilizer fuse and the antenna ring around the ignition switch before suspecting the ECM.
• Toyota: Defines P1625 as an 'Idle Signal Transmitter Circuit Malfunction,' a fault in the communication circuit between the ECM and the injector driver unit (EDU).
• BMW: Refers to a problem with the 'Pedal Position Sensor Potentiometer Supply', which is critical for the drive-by-wire throttle control.
• SAAB: Indicates 'No Bus data From TC/ABS', pointing to a communication network problem rather than a PCM power supply issue.

Real Owner Stories

2008 Suzuki Swift Diesel with crank-no-start

Vehicle cranked but did not start. The immobilizer light flashed, and a scan tool showed an active P1625 'Antenna Malfunction' code.

What they tried:

1. Technicians checked extensive wiring harnesses without success.

Outcome: A technician checked the fuse box and found a single blown fuse. Replacing the fuse immediately resolved the issue, and the car started properly.

Lesson: On Suzuki models, P1625 almost always points to the immobilizer. Always check simple, high-failure items like fuses before inspecting complex wiring.

2013 Citroën Berlingo 1.6 HDI with intermittent stalling

On cold mornings, the van started fine but stalled after 20 seconds, flashing 'ENGINE FAULT'. It repeated this 3-4 times and then drove normally.

What they tried:

1. The owner scanned the vehicle and found code P1625. Freeze frame data showed the battery voltage during starting dropped to 8.2V.

Outcome: The extremely low cranking voltage caused the ECU to reboot with a software error. The root cause was a weak battery failing under cold conditions.

Lesson: Pay close attention to freeze frame data. A battery that seems fine in warm weather fails under cold conditions, triggering power-loss codes.

2016 Peugeot 2008 1.6 BlueHDI with sudden power loss

While driving on the highway, the vehicle suddenly lost power and jerked. Turning the car off and on temporarily resolved the issue.

What they tried:

1. The owner replaced the battery and crankshaft position sensor. A shop refurbished the injectors, which did not fix the problem.

Outcome: The vehicle threw P1625 and P1621, indicating an internal ECU fault. The actual problem was a critical wiring/ground issue to the ECU, not fuel system components.

Lesson: When codes point to an internal computer fault, throwing fuel system parts at the problem is a costly mistake. Focus on ECU power, grounds, and connector integrity.

How to Prevent This Code From Triggering

• Clean Battery Terminals and Posts Annually (Every 12 months or with every oil change) — Corrosion on battery terminals acts as a resistor, impeding current flow and causing voltage drops that trigger P1625. Cleaning ensures a solid connection.
• Periodically Test Battery Health (Annually, especially for batteries over 3 years old) — A battery's ability to hold a charge diminishes over time. An annual load test identifies a weak battery before it fails a cold-start cranking test.
• Inspect and Tighten Main Ground Connections (Every 2-3 years or when working in the engine bay) — Main ground straps are critical for electrical stability. Vibrations loosen them over time, and a loose ground is a common cause of intermittent power loss.
• Use a Battery Tender for Stored Vehicles (For any storage period longer than two weeks) — Prevents the battery from self-discharging to a critically low level, avoiding sulfation that permanently damages the battery.
• Avoid Frequent Short Trips (Daily habit) — Short drives under 20 minutes fail to fully replenish the electrical charge used to start the engine, leading to a chronically undercharged battery.

Frequently Asked Questions

Can I fix P1625 myself?

Yes, many of the most common causes are DIY-friendly. Cleaning battery terminals, replacing a weak battery, and swapping a plug-in PCM relay are all beginner-level tasks that solve a majority of P1625 issues.

What is the most common misdiagnosis for P1625?

There are two major misdiagnoses. The first is replacing the PCM without performing thorough electrical tests; the PCM is usually the victim, not the cause. The second is failing to check the manufacturer-specific definition, leading to wasted time on the wrong system.

My battery is new, so why did I get a P1625 code?

A new battery doesn't guarantee a perfect electrical system. Loose terminal clamps, a corroded chassis ground, a faulty alternator, or a failing PCM relay all interrupt power and trigger the code despite a healthy battery.

Can a bad ground wire really cause this much trouble?

Absolutely. A loose, rusty, or broken ground strap is equivalent to disconnecting the power and causes the PCM to reset. A voltage drop test reading of more than 0.1V on a ground connection confirms this problem.

How do I fix P1625 on a Suzuki Swift or Grand Vitara?

For these models, the code almost always means 'Immobilizer Antenna Malfunction'. Before doing anything else, check the fuses related to the immobilizer system. If fuses are good, inspect the wiring and connector for the antenna ring around the ignition key cylinder.

Why does my car sometimes start and sometimes not with this code?

This indicates an intermittent fault. The most likely causes are a relay with failing internal contacts, a loose wire that makes and breaks connection as the car vibrates, or a worn ignition switch.

Can jump starting my car cause a P1625 code?

Yes. If the jump start is performed incorrectly (e.g., reversing polarity) or if the host vehicle has a poorly regulated alternator, it creates a voltage spike. This surge either damages the PCM or causes it to reboot, logging the code.

Will clearing the code fix the problem?

No. P1625 indicates a real electrical event occurred. Clearing the code turns the check engine light off temporarily, but it returns as soon as the underlying electrical fault happens again.

Key Takeaways

• Verify your vehicle's specific P1625 definition before replacing parts, as it means 'PCM Power Loss' on a Honda but 'Immobilizer Failure' on a Suzuki.
• Do not drive the vehicle if P1625 indicates a PCM power loss, because the engine stalls without warning at any speed and disables power steering.
• Test your battery cranking voltage first; if it drops below 9.6 volts during startup, the weak battery is causing the PCM to reset.
• Never replace the Powertrain Control Module (PCM) without first performing a voltage drop test to confirm ground connections read under 0.1 volts.