OBD-II Code U1605: CAN Bus Communication Failure

What Does U1605 Mean?

U1605 is a manufacturer-specific code indicating a loss of communication on the vehicle's Controller Area Network (CAN bus). This network acts as the vehicle's nervous system, allowing different computers (modules) to share data. When this code triggers, one or more modules fail to send or receive messages correctly, causing immediate and unpredictable electrical failures.

Technical definition: The SAE/ISO definition for U1605 varies significantly by manufacturer. It generally flags a Controller Area Network (CAN) Bus communication error, pointing to a specific module that is offline or transmitting invalid data. On Chrysler vehicles, it flags a lost connection with the Totally Integrated Power Module (TIPM). On Fiat models, it points to a faulty Blue&Me module. Other brands use similar 'P' codes (e.g., P1605) or 'C' codes (e.g., C1605) for entirely different faults.

Can I Drive With U1605?

Yes, But With Caution. Driving is possible but highly dangerous. The engine stalls unexpectedly at highway speeds or in traffic. Critical safety systems like ABS, stability control, and airbags disable, and the instrument cluster goes blank. Tow the vehicle to a repair shop immediately.

Common Causes

• Faulty Totally Integrated Power Module (TIPM) (Very Common) — On Chrysler, Dodge, and Jeep vehicles, the TIPM (the main fuse and relay box) is the primary culprit. Internal circuit board failures disrupt communication across the entire vehicle network, causing widespread electrical issues.
• Improperly Installed Aftermarket Electronics (Common) — Poorly installed remote starters, alarm systems, or aftermarket radios frequently short the CAN bus. If these devices tap into network wires incorrectly, they block signals, force modules offline, and trigger communication codes.
• Damaged or Corroded Wiring/Connectors (Common) — The CAN bus relies on a pair of twisted wires running throughout the vehicle. Damage from accidents, rodents, or connector corrosion breaks the circuit. Harnesses near the engine, behind the dashboard, and at major connection points are highly susceptible.
• Failing or Weak Battery / Bad Ground Connection (Common) — Low battery voltage or a poor chassis ground causes modules to malfunction, send erratic signals, or shut down completely. GM specifically notes poor ground connections as a root cause for network failures in several service bulletins.
• Faulty Blue&Me / Convergence Telematics Module (CTM) (Less Common) — On Fiat and Alfa Romeo models, the Blue&Me module controlling Bluetooth and USB functions is a known failure point. It causes a parasitic battery drain, a flashing odometer, and triggers CAN bus communication codes.
• Faulty Control Module (ECU, BCM, etc.) (Less Common) — Any single computer module on the network fails internally over time. A failed module stops communicating or 'shouts' corrupted data on the network, preventing other modules from talking.
🎬 Watch this guide on troubleshooting complex CAN communication faults.
• Blown Fuse for a Control Module (Less Common) — If a fuse powering a specific control module blows, that module goes offline immediately. Other modules then report they can no longer communicate with it.
• Faulty CAN Bus Terminating Resistor (Rare) — The CAN bus utilizes a 120-ohm resistor at each end of the network, often integrated into the PCM or instrument cluster. If one resistor fails, total network resistance shifts from 60 ohms to 120 ohms, crashing communication.

Symptoms

• Engine Stalling or No-Start Condition — The engine cranks but refuses to start, or stalls abruptly while driving because the engine computer loses communication with the fuel pump.
• Unpredictable Electrical Issues — Wipers turn on by themselves, the horn blares randomly, power windows fail, or dashboard lights flicker uncontrollably.
• Loss of Power Accessories — The radio, HVAC controls, and power seats stop working intermittently or shut down completely.
• Incorrect Instrument Gauge Readings — The speedometer, tachometer, fuel gauge, or temperature gauge behave erratically or drop to zero while driving.
• Check Engine Light and Other Warning Lights (also visible on scanner) — The Check Engine Light illuminates, accompanied by ABS, traction control, and airbag warning lights.

Diagnostic Flowchart

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

Common Fixes & Costs

• Repair or Replace Totally Integrated Power Module (TIPM) — Parts: $250-$500 (for a rebuilt unit), Labor: $200-$300, ~1.5 hr book time (Intermediate)
• Remove or Repair Faulty Aftermarket Electronics — Parts: $0-$20, Labor: $150-$500, ~2.5 hr book time (Intermediate)
• Replace Battery and Clean Terminals/Grounds — Parts: $150-$350, Labor: $50-$150, ~0.8 hr book time (DIY)
• Repair Damaged CAN Bus Wiring — Parts: $10-$50, Labor: $300-$1000+, ~4 hr book time (Professional)
• Replace a Faulty Control Module (e.g., ECM, BCM, TCM) — Parts: $300-$2000+, Labor: $150-$400, ~1.5 hr book time (Professional)

Used vs. New Parts: Buying Guide

When a used part is worth it: A used TIPM from a junkyard is a high-risk, low-cost option. It makes sense only for tight budgets on older vehicles. Be aware that a used TIPM likely has the same inherent flaws or is close to failure itself.

Donor-vehicle mileage cap: roughly under 60000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Match the part number exactly.
• Source from a vehicle of the same year or newer.
• Visually inspect for corrosion, water damage, or melted connectors.
• Avoid parts from vehicles involved in front-end collisions or floods.

Decision logic:

• If The vehicle is critical for daily use and reliability is paramount. → Buy a new OEM or a professionally rebuilt TIPM with a long warranty.
• If The budget is extremely limited and you accept the risk of premature failure. → A used TIPM is a viable gamble, but expect a short warranty.
• If You want a balance of cost savings and reliability. → A rebuilt TIPM from a reputable company is the best choice, offering corrected internal flaws and a solid warranty for less than a new OEM part.

Warranty tradeoff: Used parts typically offer a 30-90 day warranty. Rebuilt units from specialists come with a 1-year to lifetime warranty. New OEM parts carry a 1-2 year manufacturer's warranty.

Worst-case if a used part fails: $500-$1000 if a used or poorly rebuilt part fails, including the cost of another replacement part plus repeat diagnostic and labor charges.

What Happens If You Wait — Timeline

1. 0-2 weeks: Intermittent issues begin. A single, brief stall while driving. The radio cuts out and comes back. A warning light flashes on and then goes off. (MPG impact: 0%% · Added cost: $0)
2. 2 weeks - 3 months: Symptoms become more frequent. The vehicle requires multiple crank attempts to start. Stalling becomes common. A parasitic drain begins, causing a weak or dead battery. (MPG impact: N/A (Reliability impact is high)% · Added cost: $150-$350 (for a new battery killed by the parasitic drain and stress from repeated hard starts))
3. 3-6 months: Cascading failures begin. The vehicle is unreliable, frequently stalling or refusing to start. Constant voltage fluctuations stress other electronic modules. The vehicle is unsafe to drive. (MPG impact: N/A (Vehicle is often undriveable)% · Added cost: $200-$500 (for towing and emergency diagnostic fees))
4. 6+ months: Permanent damage to other modules occurs. A shorted CAN bus or failing power module sends voltage spikes that destroy expensive computers (PCM, BCM, ABS module). (MPG impact: N/A% · Added cost: $1000-$3000+ (for replacement and programming of additional control modules damaged by the initial fault))

Cost of Not Fixing It

• Immediate: Extreme safety risk. The vehicle stalls unexpectedly in traffic. Safety systems like ABS and airbags disable, and the vehicle refuses to start, leaving you stranded. (Added cost: $200-$500 (for towing and emergency diagnosis))
• Weeks to Months: A faulty TIPM or module causes a parasitic battery drain, repeatedly killing the battery and shortening its lifespan. Constant voltage fluctuations stress other sensitive electronics. (Added cost: $150-$350 (for a new battery) + potential cost of other damaged modules)
• Long-Term: Continued operation with a network fault leads to cascading failures. An intermittent stall becomes a complete electrical system shutdown, destroying expensive components like the PCM or transmission control module. (Added cost: $1000-$3000+ (for replacement of major control modules))

Diagnosis Steps

1. Check the Battery and Grounds
   Ensure the battery is fully charged (above 12.4 volts) and terminals are clean. Load test the battery. Inspect the main battery-to-chassis and engine-to-chassis ground straps for corrosion or looseness.
   Tools: Multimeter, socket set, wire brush, battery load tester (Beginner)
2. Perform a Visual Inspection
   Check wiring harnesses for chafing, melting, or rodent damage near the engine and under the dash. Inspect aftermarket devices (remote starters, stereos) and their wiring quality. Look at major connectors at the main fuse box (TIPM) and Engine Control Module (ECM) for corrosion.
   Tools: Flashlight (Beginner)
3. Check Fuses
   Using the owner's manual, inspect all fuses related to control modules (PCM, BCM, ABS, TIPM). A blown fuse takes a module offline, causing a communication fault.
   Tools: Fuse puller, multimeter, owner's manual (Beginner)
4. Scan for All Codes
   Use an OBD-II scanner capable of reading codes from ALL modules. A U1605 code is often accompanied by other 'U' codes (like U0100 or U0002) that pinpoint which module is failing or confirm a total network failure.
   Tools: Advanced OBD-II Scanner (Intermediate)
5. Test the CAN Bus Resistance
   With the battery disconnected, measure resistance between Pin 6 (CAN High) and Pin 14 (CAN Low) on the OBD-II port. A healthy network reads exactly 60 ohms. A reading of 120 ohms indicates a broken wire or faulty terminating resistor. A reading near 0 ohms indicates a short circuit.
   Tools: Multimeter (Advanced)
6. Advanced Resistance Test: Check for Shorts to Ground
   With the battery disconnected, measure resistance between CAN High (Pin 6) and chassis ground (Pin 4), then between CAN Low (Pin 14) and chassis ground. Both readings must be very high (OL or mega-ohms). Low resistance indicates a short to ground.
   Tools: Multimeter (Advanced)
7. Perform a 'Wiggle Test'
   While monitoring CAN bus resistance with a multimeter, systematically wiggle wiring harnesses and connectors. If the resistance reading jumps from 60 ohms to 120 ohms or OL, you located a harness section with an open circuit.
   Tools: Multimeter, wiring diagram (Advanced)
8. Analyze the CAN Bus Waveform
   Connect a two-channel oscilloscope to CAN High (Pin 6) and CAN Low (Pin 14). A healthy bus shows mirror-image signals idling at 2.5V. During communication, CAN High jumps to 3.5V and CAN Low drops to 1.5V. A flat line indicates a short; a non-mirrored signal points to an open circuit or faulty module.
   Tools: 2-Channel Oscilloscope, OBD-II breakout box or back-pin probes (Professional)
9. Isolate the Faulty Module or Wiring
   If resistance or waveforms are incorrect, disconnect one module at a time from the CAN bus. When the reading returns to normal, the last module disconnected (or its wiring) is the source of the fault.
   Tools: Wiring diagram, multimeter, hand tools (Professional)

When This Code Triggers (Freeze-Frame Conditions)

• Fault Trigger Event: Key-On or Cranking (The code sets immediately upon vehicle startup when modules perform their initial communication check-in. A failure to respond triggers the fault.)
• Module Status: No Communication (Freeze frame data indicates which specific module (e.g., ECM, TCM, ABS) failed to respond on the network.)
• Battery Voltage: 9-12V (A weak battery causes voltage to fall below the operational threshold during cranking, causing modules to drop off the network.)
• Vehicle State: Any (A CAN bus failure occurs under any condition: idle, cruise, or acceleration, especially if the cause is a loose wire or failing module.)

Related Codes

• U0100 — 'Lost Communication With ECM/PCM'. Frequently appears with U1605. U1605 is the root cause (e.g., a failed TIPM), and U0100 is the symptom because the TIPM fails to power the ECM.
• U0001 — 'High Speed CAN Communication Bus' fault. U0001 means the bus itself is malfunctioning (shorted wires), while U1605 points towards the specific module causing that malfunction.
• U0002 — 'High Speed CAN Communication Bus Performance'. U0002 suggests the network is active but degraded by electrical noise or high resistance, whereas U1605 often indicates a hard failure.
• P1605 (on Toyota/Ford) — NOT the same as U1605. On Toyota, P1605 means 'Rough Idling Malfunction'. On Ford, it means 'Keep Alive Memory (KAM) Test Failure'. Diagnosing P1605 involves checking vacuum leaks or battery connections, not CAN bus wiring.

Climate & Environmental Factors

• Humidity and Moisture: Moisture penetrates poorly sealed connectors or modules like the TIPM, causing circuit board corrosion, increasing resistance, and failing communication networks.
• Road Salt (Salt Belt Regions): Salt spray attacks electrical grounds, wiring harnesses, and the TIPM, rapidly accelerating corrosion and network failure.
• Extreme Cold: Reduces battery efficiency, causing voltage drops during startup that prevent modules from initializing correctly. Cold also makes wires and plastic connectors brittle.
• Extreme Heat: Increases under-hood temperatures, accelerating the degradation of electronic components within modules and increasing internal resistance.

How to Clear the Code After You Fix It

1. Ensure all repairs are complete and the battery is fully charged.
2. Use a capable OBD-II scan tool to command a 'Clear All Codes' function.
3. Perform a 'hard reset' by disconnecting the negative battery terminal for at least 15 minutes. For Chrysler vehicles, touch the disconnected negative cable to the positive terminal for 30 seconds to drain residual power.
4. Perform the manufacturer-specific drive cycle to allow readiness monitors to run.

Drive cycle (~20 minutes): A general Chrysler drive cycle includes: 1. Cold start and idle for 5 minutes. 2. Drive at a steady speed between 40-60 mph for 8 minutes. 3. Stop and idle for 3 minutes. 4. Drive at a speed over 20 mph for 2 minutes. 5. Turn the vehicle off for 10 minutes.

Readiness monitors affected: Comprehensive Component Monitor, Misfire Monitor

Before emissions retest: drive at least 50 miles to fully set monitors.

Watch out for:

• Simply clearing the code with a scanner will not fix the underlying hardware issue; the code returns immediately.
• Failure to perform a full drive cycle leaves OBD-II readiness monitors in a 'Not Ready' state, causing an emissions test failure.
• Not addressing the root cause (e.g., a bad TIPM, corroded wire) leads to the code reappearing.

Will This Fail Emissions / State Inspection?

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

• California: An illuminated Check Engine Light from a U1605 code is an automatic failure. After repair, a full drive cycle must be completed to set the readiness monitors before a re-test.
• New York: Any fault code that turns on the Malfunction Indicator Lamp (MIL), including U1605, results in an immediate inspection failure.
• Texas: An illuminated Check Engine Light is an automatic failure. After clearing the code, drive the vehicle 50-100 miles to ensure readiness monitors are set.

Most Commonly Affected Vehicles

• Chrysler Town & Country (2008-2016) — Highly prone to TIPM failure, the primary cause of network communication codes on this platform.
• Dodge Grand Caravan (2008-2020) — Shares the problematic TIPM with Chrysler. Rebuilt TIPMs are the standard fix.
• Jeep Grand Cherokee (2005-2013) — Frequently experiences TIPM-related electrical and communication faults resulting in no-start conditions.
• Fiat 500, Panda, Punto (2007-2021) — A faulty Blue&Me (Convergence Telematics) module is a very common cause of CAN network failure, presenting with a flashing odometer and dead battery.
• Volkswagen Jetta, Golf, Passat (2010-2018) — VW typically uses code P1605 for internal ECU errors, presenting similar no-start or stalling symptoms.
• Subaru Outback, Legacy (2015-2019) — Subject to recalls for issues affecting vehicle electronics, such as faulty fuel pumps or ESC systems leading to communication errors.
• Land Rover Freelander (2002-2005) — Code P1605 points to an 'Internal EEPROM Fault' within the Transmission Control Module (TCM).
• Mitsubishi Various (2000-2012) — U1605 is defined as 'MSCK short', indicating a specific circuit fault within the network.

Manufacturer-Specific Notes

• Chrysler / Dodge / Jeep / Ram: This code is almost exclusively related to a failing Totally Integrated Power Module (TIPM). Symptoms are bizarre and random, from the fuel pump running continuously to wipers activating on their own.
• Fiat / Alfa Romeo: A common cause for CAN bus faults and a flashing odometer is the failure of the Convergence Telematics Module (CTM), known as the Blue&Me module. Disconnecting it is the first diagnostic step.
• Ford: Ford uses P1605 for 'Keep Alive Memory (KAM) Test Failure', meaning the Powertrain Control Module (PCM) lost its constant 12v power supply due to a blown fuse or bad battery.
• Toyota: Toyota uses P1605 for 'Rough Idling' or 'Startability Malfunction'. It triggers when engine RPM drops too low after starting, caused by vacuum leaks or a dirty throttle body.
• General Motors (Chevrolet/GMC): GM rarely uses U1605. Network communication issues trigger a host of other 'U' codes and are frequently related to poor grounds (TSB 18-NA-161).
• Honda: U1605 is not a standard Honda code. Communication issues trigger codes like U0028 or U0073 (F-CAN Communication Error), often requiring a reset with an advanced scan tool after an accident.

Real Owner Stories

2011 Jeep Grand Cherokee stalls randomly, no-start

Owner reported the engine shut off unexpectedly while driving. Often accompanied by a no-crank, no-start condition. No specific codes were always present.

Outcome: The root cause was a faulty Totally Integrated Power Module (TIPM). Specifically, the internal fuel pump relay failed, cutting power to the engine. Installing an external fuel pump relay bypass kit resolved the stalling and no-start issues.

Lesson: On a 2011-2013 Chrysler/Dodge/Jeep product with random stalling or no-start issues, the TIPM is the primary suspect. An external relay bypass is a common, cost-effective fix compared to full TIPM replacement.

2012 Fiat 500 with flashing odometer and battery drain

Owner found the odometer flashing continuously, steering wheel buttons unresponsive, and the battery dead after sitting for a day.

Outcome: The failure was traced to the Blue&Me telematics module. The module failed internally and stayed 'awake,' causing the parasitic drain and disrupting CAN bus communication. The owner disconnected the faulty module and performed a 'proxy alignment' with MultiECUScan software, stopping the flashing and battery drain.

Lesson: A flashing odometer on a Fiat is a hallmark symptom of a CAN bus network problem. Before replacing expensive components, perform a parasitic draw test and try disconnecting the Blue&Me module.

2013 Dodge Avenger won't start after aftermarket radio install

Vehicle ran fine until an aftermarket stereo was installed. After wiring the new head unit, the car would not crank or start. The OBD-II port was dead.

Outcome: The aftermarket wiring harness was wired incorrectly, shorting a CAN bus wire to a power wire. This single short circuit brought down the entire vehicle communication network. The fix required removing the aftermarket harness and restoring the original factory connections.

Lesson: Never assume an aftermarket wiring harness is correct. Improperly tapping into CAN bus wires is a very common cause of no-start conditions and network failure after a stereo installation.

How to Prevent This Code From Triggering

• Periodically Clean and Protect Battery Terminals and Ground Straps (Every 12 months or during oil change) — Corrosion on battery terminals or main chassis grounds increases resistance, causing voltage drops that make electronic modules behave erratically or fail to initialize at startup.
• Keep the TIPM and Engine Bay Connectors Dry (During vehicle use and cleaning) — Moisture is a primary cause of TIPM and module failures. Avoid high-pressure washing the engine bay. Ensure the TIPM cover is securely latched to prevent water intrusion.
• Apply Dielectric Grease to Critical Connectors (When servicing or replacing components) — When connectors are exposed, applying dielectric grease seals out moisture and oxygen, preventing pin corrosion that causes high resistance and network faults.
• Use Caution with Aftermarket Electronics (During installation of any non-factory part) — Improperly installed accessories create electrical noise or short the bus wires. Always use high-quality wiring adapters and never use 'T-taps' on network wires.

Frequently Asked Questions

Can I fix a U1605 code myself?

You can perform basic fixes like replacing the battery, checking fuses, and removing aftermarket stereos. However, diagnosing the CAN bus with a multimeter or replacing a major module like the TIPM requires specialized tools. Stop DIYing and hire a professional if basic visual and voltage checks do not reveal the problem.

What is the most common misdiagnosis for a U1605?

Mechanics frequently replace expensive control modules like the ECM without performing a thorough wiring diagnosis. Always rule out a weak battery, bad grounds, and faulty aftermarket accessories before condemning a $500 module.

How much does it cost to diagnose a U1605 code?

Shops charge a diagnostic fee for complex electrical issues, typically ranging from 1.5 to 3 hours of labor. Expect to pay between $200 and $450 for a proper network communication diagnosis.

Will clearing the code fix the problem?

No. Clearing the code only turns off the check engine light temporarily. Because U1605 stems from a hard physical fault like a broken wire or dead module, the code returns immediately upon startup.

My scanner shows P1605, not U1605. Is it the same thing?

No. A 'U' code indicates a network communication problem between modules. A 'P' code (Powertrain) like P1605 on a Toyota or Ford points to specific engine performance or computer memory issues, requiring a completely different diagnostic approach.

Can a bad key fob or ignition switch cause a U1605?

A failing key fob or mechanical ignition switch does not directly cause a U1605 network code. However, a failing Wireless Control Module (WCM) that reads the key can crash the network and trigger communication codes on certain vehicles.

What should a healthy CAN bus signal look like on an oscilloscope?

A high-speed CAN bus displays two clean, mirror-image square wave patterns resting at 2.5 volts. During communication, CAN High jumps to 3.5 volts while CAN Low drops to 1.5 volts. The signals must be sharp and free of distortion.

Key Takeaways

• On 2008-2020 Chrysler, Dodge, and Jeep vehicles, U1605 almost always indicates a failing Totally Integrated Power Module (TIPM) requiring a $250-$500 rebuilt replacement.
• Disconnect any aftermarket stereos or remote starters installed within the last 30 days, as improper wiring frequently shorts the CAN bus and triggers this code.
• Measure the resistance between OBD-II pins 6 and 14 with the battery disconnected; a healthy network reads exactly 60 ohms, while 120 ohms indicates a broken wire or failed module.
• Do not confuse the network communication code U1605 with the powertrain code P1605, which diagnoses a rough idle on Toyota or a memory failure on Ford vehicles.