P0688 on 2019-2022 Ram 1500: Causes and Fixes for the Auto Shutdown Relay Circuit

What's Unique About the 2019-2022 Ram 1500

For this generation of Ram 1500, the P0688 code is frequently a secondary code, not the primary fault. The issue often stems from a shorted component, most commonly an ignition coil, which blows a fuse. This single fuse (often F63 or F90) provides power to both the ignition coils AND the ASD relay's sense circuit. So, when the coil shorts and blows the fuse, the PCM loses the sense circuit voltage. It incorrectly interprets this as a relay failure and sets P0688, even though the relay itself may be perfectly fine. This makes checking specific fuses the most critical first step, as documented in numerous owner forums and TSBs.

Diagnostic Flowchart

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

Symptoms You May Notice

• Engine cranks but will not start.
• Engine does not crank at all (no-crank, no-start).
• Check Engine Light is illuminated.
• Red lightning bolt (Electronic Throttle Control warning) on the dash.
• Vehicle stalls while driving.
• Loss of power to fuel injectors and ignition coils.
• No audible 'buzz' from the fuel pump when the key is turned.

Most Likely Causes

1. Blown Fuse (F63, F90, or similar) 🔴 High Probability The ASD sense circuit is often tied to the ignition coils on a shared fuse. A short in an ignition coil is common and will blow this fuse, cutting power to the sense circuit and triggering the code. Forum users on '5thgenrams.com' specifically identify the 10A F63 fuse as the most common culprit 🎬 Watch: How to diagnose the ASD sense circuit and misfires. for the 5.7L Hemi.
   How to confirm: Locate the Power Distribution Center (fuse box) in the engine compartment. Visually inspect and test fuses F63 (10A) and F90 (25A), which are commonly linked to the ignition coils and ASD circuit. A multimeter is the best tool for testing.
   Typical fix: Replace the blown fuse. If the fuse blows again immediately, there is an underlying short circuit that must be diagnosed. The most likely cause is a cracked ignition coil shorting to the engine block.
   Est. part cost: $1-$5
2. Faulty Ignition Coil 🔴 High Probability The plastic housing on the ignition coils can develop cracks over time due to heat and vibration. This allows high voltage to arc to the engine block (ground), creating a short circuit that blows the fuse shared with the ASD sense circuit.
   How to confirm: If the fuse for the ignition coils (e.g., F63) is blown, unplug all ignition coils. Replace the fuse. If it does not blow, plug in one coil at a time until the fuse blows again, identifying the faulty coil. Visually inspect each coil for cracks, melting, or burn marks.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace the spark plug for that cylinder 🎬 See this walkthrough on how to replace your ignition coils. at the same time.
   Est. part cost: $40-$80 per coil
3. Faulty Auto Shutdown (ASD) Relay 🟡 Medium Probability Relays are electro-mechanical switches that can wear out over time from heat cycles and repeated use, leading to internal failure where the switch no longer makes contact or the coil burns out.
   How to confirm: The easiest way to test is to swap the ASD relay with an identical, known-good relay from a non-critical system (like the horn or HVAC blower relay) in the same fuse box. If the truck starts, the original ASD relay is bad.
   Typical fix: Replace the ASD relay. A common Mopar part number is 68271210AA, but always verify for your specific vehicle.
   Est. part cost: $15-$40
4. Wiring or Connector Issues ⚪ Low Probability Engine bay wiring harnesses are exposed to heat, vibration, and potential abrasion. Wires can chafe against brackets or other components, causing a short to ground that can blow the ASD fuse or cause an open in the sense circuit.
   How to confirm: Visually inspect the wiring harness leading from the fuse box to the PCM and ignition coils. Look for any signs of chafing, melting, or corrosion. A 'wiggle test' (wiggling the harness while the engine is idling, if it runs) can sometimes replicate the fault. A multimeter is needed 🎬 Watch: Finding a broken harness wire causing a P0688 code. to check for continuity on the sense circuit wire between the fuse box and the PCM.
   Typical fix: Repair the damaged section of wire or clean/replace the corroded connector.
   Est. part cost: $5-$50

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): This is the least likely cause and should only be considered after all other possibilities (fuses, coils, relay, wiring) have been exhaustively ruled out. Replacing the PCM is expensive and requires programming by a dealer or qualified shop.

Diagnosis Steps

1. Read all stored codes with an OBD-II scanner. Note any misfire codes (P03xx) that accompany P0688.
2. Check for official TSBs related to P0688 for your specific VIN.
3. Locate the main fuse box (Power Distribution Center) in the engine bay. Inspect and test fuses F63 (10A) and F90 (25A).
4. If a fuse is blown, inspect the ignition coils for visible cracks or signs of melting. This is the likely cause of the blown fuse.
5. If fuses are good, swap the ASD relay with a known-good, identical relay (e.g., horn relay) and attempt to start the engine.
6. If the issue persists, inspect the wiring and connectors between the fuse box, ignition coils, and the PCM for any visible damage, corrosion, or looseness. Perform a 'wiggle test' on the harness if possible.
7. Using a multimeter and a wiring diagram, verify voltage and continuity on the ASD relay sense circuit (Pin 1, F344 circuit on some models) between the fuse box and the PCM.
8. If all other components and wiring test good, the PCM may be the issue, but this should be confirmed by a professional technician.

Parts You'll Likely Need

• Automotive Fuse — A blown fuse is a highly common cause for this code, as a short in a related component like an ignition coil will cause the fuse to blow, cutting power to the sense circuit.
  Trusted brands: Bussmann, Littelfuse
  OEM price range: $1-$5
  Aftermarket price range: $1-$5
• Ignition Coil — A cracked and shorting ignition coil is a very common root cause for the blown fuse that triggers P0688.
  Trusted brands: Mopar, NGK, Standard Motor Products
  OEM price range: $60-$90
  Aftermarket price range: $40-$70
• Auto Shutdown (ASD) Relay (OEM #68271210AA) — The relay itself can fail internally, preventing it from correctly powering its circuits or sending the confirmation signal to the PCM.
  Trusted brands: Mopar, Bosch, Standard Motor Products
  OEM price range: $25-$50
  Aftermarket price range: $15-$40

Related Codes That Often Appear With This One

• P0685 — This code, 'ECM/PCM Power Relay Control Circuit / Open,' is closely related and points to the control (coil) side of the relay, while P0688 points to the feedback/sense side. They often appear together when there's a general failure in the relay's operation or its power supply.
• P03xx (e.g., P0307) — If a faulty ignition coil is shorting out and blowing the fuse that protects the ASD sense circuit, you will very likely also see a misfire code for that specific cylinder (e.g., P0307 for cylinder 7). This is a strong indicator that the coil is the root cause.

Technical Service Bulletins (TSBs) & Recalls

• S1918000013 Rev. A (2021-10-06): 'No Crank No Start Condition. P0688 - Auto Shutdown Relay Sense Circuit Low Found In The PCM'
• S1918000013 Rev. B (2023-01-14): 'Crank, No Start Condition, Diagnostic Trouble Code (DTC) P0688 - Auto Shutdown Relay Sense Circuit'

Platform-Specific Known Issues

• A 'No Crank No Start Condition' or 'Crank, No Start Condition' linked to DTC P0688 has been documented by the manufacturer in Technical Service Bulletins for this vehicle range.
• The root cause is frequently a shorted ignition coil blowing the F63 or F90 fuse, which also powers the ASD sense circuit, making P0688 a secondary fault code.

Mechanic-Grade Diagnostic Values

• ASD Relay Sense Circuit Voltage at PCM — expected: Battery voltage (approx. 12V) when the ASD relay is commanded ON by the PCM.. Failure: 0V or significantly low voltage when the relay should be active. This directly triggers P0688.
• ASD Relay Coil Resistance — expected: 75 ohms +/- 5 ohms between terminals 85 and 86 of the relay.. Failure: A reading outside this range indicates a faulty relay coil.
• Ignition Coil Primary Resistance (5.7L Hemi) — expected: Approximately 0.6 to 0.8 ohms.. Failure: An open circuit (infinite resistance) or a reading significantly different from other coils on the engine. OEM specs are not always published, so comparison is key.
• Ignition Coil Secondary Resistance (5.7L Hemi) — expected: Approximately 12k ohms.. Failure: A reading that is substantially different from a known-good coil.

Scan Tool Commands That Help

• wiTECH or high-end bidirectional scanner: ASD Relay Actuation / Output State Test — This command allows a technician to manually command the PCM to energize the ASD relay. While monitoring voltage at the PCM sense pin (Pin 1), activating the relay should show battery voltage. If the relay clicks but no voltage appears at the sense pin, it confirms a wiring or fuse issue between the relay output and the PCM.

Wiring & Ground Locations

• PCM Connector C1, Pin 1 — This is the main connector at the Powertrain Control Module (PCM), located in the engine bay.. This specific pin is the 'Auto Shutdown Relay Sense Circuit' input. It's the wire the PCM 'watches' to confirm the ASD relay is working. On many 5.7L models, this is a Brown/Gray (BN/GY) wire on the F344 circuit. If there is no voltage here when the relay is on, the PCM sets code P0688.
• Fuse F63 (10A) — Located in the Power Distribution Center (PDC) or main fuse box in the engine compartment.. This fuse commonly powers the ignition coils but also provides the voltage source for the ASD sense circuit. A shorted ignition coil will blow this fuse, which cuts power to the sense pin on the PCM, directly causing P0688 even if the relay is good.
• Main Engine/Battery Ground — The primary ground cable runs from the battery negative terminal to the engine block and chassis. There was a customer satisfaction campaign (W14) for some 2020 3.0L Diesel models for an incorrect length ground bolt causing a no-start, though not directly tied to P0688.. A poor main ground connection can cause widespread, erratic electrical issues, including voltage drops that could potentially confuse the PCM and trigger power relay sense codes. Ensuring the main ground connections are clean and tight is a fundamental step.

Real Owner Repair Stories

• 5thgenrams.com forum user 'SavageHacker117' (2018 Ram 1500 5.7L (applies directly to 2019+ DT generation wiring)) — Crank, no start, no ignition coil or fuel injector pulse, with DTC P0688 set.
  ❌ Tried (didn't work) Initial diagnosis was confusing due to checking the wrong PCM pin (Pin 37 showed 12V, but was not the correct sense line for this configuration).
  ✅ What actually fixed it The root cause was a blown 10A fuse in location F63, which protects the ignition coils. This same fuse supplies power to the ASD sense circuit on PCM Pin 1 (Brown/Gray wire). Replacing the fuse restored voltage to the sense circuit, cleared the P0688 code, and allowed the truck to start. The underlying cause of the blown fuse was presumed to be a faulty ignition coil.
• YouTube video by 'Tony Fix it' (2010 Ram 1500 (similar wiring principles)) — Crank no-start with code P0688. A 25A ASD fuse was found blown.
  ❌ Tried (didn't work) Initially replacing the fuse allowed the truck to start, but the problem returned.
  ✅ What actually fixed it A 'wiggle test' on the main engine wiring harness caused the truck to stall. Further inspection revealed a broken Brown/Yellow wire inside the harness loom. The wire had corroded and broken, creating an open circuit that overloaded the ASD system. Repairing the broken wire by soldering in a new section permanently fixed the issue.

Model Year Variations Within This Range

• 2022: The 2022 model year introduced the Uconnect 5 infotainment system for Big Horn trims and up. While this does not directly affect the P0688 fault logic, it represents a significant change in the vehicle's overall electronic architecture compared to the 2019-2021 models which used Uconnect 4.