P0604 on 2008-2015 GMC Sierra 1500: RAM Error Causes and Fixes

What's Unique About the 2008-2015 Gmc SIERRA 1500

While P0604 is a generic code, its appearance on the 2008-2015 Sierra has specific guidance from GM. Manufacturer bulletins direct technicians to investigate the Transmission Control Module (TCM) when this code is present, often in conjunction with other module-related codes. [Bulletin #PIP4653E, 21] This suggests that the TCM is a more common point of failure for this error than the main engine computer (PCM) on these trucks. The TCM is often a Transmission Electro-Hydraulic Control Module (TEHCM), located inside the transmission oil pan 🎬 Watch: How to repair the TEHCM pressure switch membrane., making its replacement more labor-intensive than a typical external module.

Diagnostic Flowchart

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

Generation note: This year range covers two Sierra 1500 generations: the GMT900 (2008-2013/14) and the K2XX (2014-2015). The underlying causes for P0604 are similar, but module locations, wiring, and part numbers will differ between the two generations. The provided TSBs apply to vehicles in both generations.

Symptoms You May Notice

• Check Engine Light is on
• Transmission may shift harshly or erratically
• Engine may stall, hesitate, or fail to start
• ABS or Traction Control lights may illuminate
• Vehicle may enter a reduced power mode
• Gear position indicator on the dashboard may be blank or incorrect

Most Likely Causes

1. Low Battery Voltage or Weak Battery 🔴 High Probability → Shop Vehicle Battery Control modules require a stable voltage to maintain their Keep Alive Memory (KAM). A weak battery, especially during engine cranking, can cause voltage to drop low enough to corrupt the RAM and trigger a P0604 code. This can also erase adaptive strategies, leading to poor idle after a battery change until the system relearns.
   How to confirm: Test the battery with a digital multimeter or an electronic battery tester. A healthy, fully charged battery should read approximately 12.6 volts with the engine off. With the engine running, the alternator should be charging it at around 13.5-14.8 volts.
   Typical fix: Replace the vehicle's battery.
   Est. part cost: $150-$350
2. Loose or Corroded Battery Terminals and Grounds 🟡 Medium Probability → Shop Vehicle Battery Corrosion or loose connections at the battery, or on the main engine and chassis ground straps, can create voltage drops that mimic a failing battery, leading to memory errors in the modules. These trucks have several key ground points on the frame and engine block that are exposed to the elements.
   How to confirm: Visually inspect the battery terminals for white or blue-green corrosion. Ensure the terminal clamps are tight and cannot be moved by hand. Follow the negative battery cable to its connection point on the chassis and the engine block to check for tightness and corrosion. A voltage drop test across the ground cables should show minimal resistance (less than 0.1 Ω).
   Typical fix: Clean the battery terminals and cable ends with a wire brush. Tighten all connections. Replace corroded cable ends or ground straps if necessary.
   Est. part cost: $5-$50
3. Faulty Transmission Control Module (TCM) 🟡 Medium Probability → Shop Transmission Assembly GM Technical Service Bulletin #PIP4653E specifically points to the TCM as a potential source for P0604 on these trucks, indicating a known issue. For the common 6L80 transmission, the TCM is part of the TEHCM (Transmission Electro-Hydraulic Control Module) located inside the transmission pan, exposed to heat and fluid, which can lead to failure.
   How to confirm: This requires a professional scan tool to check for communication with the TCM and to see if the code is stored specifically within that module. Diagnosis involves ruling out all power and ground issues first. If communication is lost (U0101), the TCM is a strong suspect.
   Typical fix: Replace the Transmission Control Module (TEHCM) and have it programmed to the vehicle's VIN. This requires dropping the transmission pan.
   Est. part cost: $300-$700
4. Faulty Powertrain Control Module (PCM) ⚪ Low Probability → Shop Engine Control Module (ECM) While less common than power supply issues, the PCM itself can fail internally, causing a RAM error. This is often a last resort after all other possibilities have been exhausted. One owner reported this as the final fix after verifying the charging system was working correctly.
   How to confirm: After confirming the battery, charging system, and all related wiring are in perfect condition, the PCM becomes the primary suspect. A technician may attempt to re-flash the PCM with updated software before condemning the module. If the code returns immediately after clearing, a hardware fault is likely.
   Typical fix: Replace the PCM and perform the necessary programming and relearn procedures (crankshaft position, theft deterrent, etc.).
   Est. part cost: $400-$900

Rare But Worth Checking

• Aftermarket Tuner/Programmer: If an aftermarket performance tune has been installed, it can sometimes cause conflicts with the module's software, leading to memory errors. Reverting to the stock tune can sometimes resolve the issue.
• Wiring Harness Damage: Damage to the wiring harness providing power or ground to the PCM or TCM can cause intermittent voltage issues, triggering the code. This can be caused by chafing, heat, or rodent damage. GM has noted issues in the communication enable circuit under the driver's sill plate in some models.

Diagnosis Steps

1. Read all stored fault codes with a quality OBD-II scanner. Note which module(s) have stored the P0604 code (e.g., ECM or TCM). This is a critical step.
2. Check Battery Health: With the engine off, measure battery voltage. It should be ~12.6V. Start the engine and measure charging voltage. It should be between 13.5V and 14.8V. A weak or failing battery is a primary cause.
3. Inspect Power and Ground Connections: Disconnect the battery. Thoroughly clean the battery posts and cable terminals. Inspect the main engine-to-chassis ground strap and body-to-frame grounds for corrosion and tightness.
4. Clear Codes and Reset Modules: With all connections clean and tight, reconnect the battery. Clear the fault codes. Some owners report success by disconnecting the battery for 30 minutes to allow all modules to fully reset.
5. Test Drive: Drive the vehicle to see if the code returns. If it does not, the issue was likely a temporary voltage problem or poor connection.
6. Check Fuses: Inspect all fuses related to the PCM, TCM, and ECM in the underhood and interior fuse panels.
7. Professional Diagnosis: If the code returns, take the vehicle to a qualified technician. They will use an advanced scan tool to confirm which module is at fault. Per TSB guidance, they may first attempt to re-flash the module with the latest software. If the re-flash fails or the code returns immediately, the module itself has likely failed and requires replacement.

Parts You'll Likely Need

• Battery — A weak or failing battery is the most common trigger for memory-related fault codes like P0604.
  Trusted brands: ACDelco, Interstate, DieHard
  OEM price range: $200-$350
  Aftermarket price range: $150-$250
• Transmission Control Module (TCM/TEHCM) (OEM #24256861 (Example for 6L80 equipped models, VIN specific)) — GM TSBs specifically identify the TCM as a likely source of this code on the Sierra. It often requires replacement if power and grounds are confirmed to be good. Part numbers are VIN-specific. For many models, this is a TEHCM located inside the transmission.
  Trusted brands: ACDelco, Dorman

Related Codes That Often Appear With This One

• P0601 — Indicates an Internal Control Module Memory Check Sum Error. It's a related internal module fault.
• P0603 — Indicates an Internal Control Module Keep Alive Memory (KAM) Error, often caused by a battery disconnect or power loss.
• U0101 — Stands for Lost Communication with TCM. This code is very common when the P0604 is originating from a failing Transmission Control Module, as the module will stop communicating on the CAN bus.
• P1621 — A GM-specific code for Control Module Long Term Memory Performance. All these codes are mentioned together in TSBs and point to an internal module or power supply problem. [Bulletin #05-06-04-060A, Bulletin #PIP4653E, 10]

Technical Service Bulletins (TSBs) & Recalls

• Bulletin #PIP4653E: Advises technicians that DTCs P0601, P0603, P0604, P062F or P1621 may be stored in the Transmission Control Module (TCM). It stresses the importance of verifying which module set the code before beginning repairs.
• Bulletin #05-06-04-060A: An informational bulletin that groups several internal control module fault codes (P0601, P0602, P0603, P0604, etc.) together. It notes that these codes can be set by various modules and that diagnosis should only begin after confirming which module is reporting the fault.

Mechanic-Grade Diagnostic Values

• Module Ground Circuit Resistance — expected: < 0.1 Ω. Failure: A reading higher than 0.1 Ohms indicates excessive resistance in the ground circuit, which can cause voltage drops and module malfunction.
• Battery Voltage (Engine Off) — expected: ~12.6 Volts. Failure: Voltage below 12.4V indicates a discharged or failing battery.
• Charging System Voltage (Engine Running) — expected: 13.5 - 14.8 Volts. Failure: Voltage below 13.5V may indicate a failing alternator; above 14.8V can damage electronics.
• Voltage at Module During Cranking — expected: > 9.0 Volts. Failure: A significant drop below 9.0V during engine start can corrupt module memory and trigger a P0604.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Module Setup / Relearn — After replacing a PCM, functions like 'Idle Learn Reset', 'Crankshaft Position Variation Learn', and 'Theft Deterrent Relearn' must be performed.
• GDS2 (GM Global Diagnostic System 2): Transmission Service Fast Learn — After replacing a TCM/TEHCM or reprogramming, this function resets and begins the relearn process for transmission shift adapts to restore proper shift quality.
• GDS2 or Tech2Win: Clear All DTCs — Used after programming a new module to clear any communication codes that were set during the flash process.

Wiring & Ground Locations

• G102 / G103 — On the cylinder heads. G103 is on the front of the passenger side cylinder head; G102 is on the driver's side.. These are primary engine grounds. While G102 mainly grounds ignition coils, G103 is a critical ground path for the ECM and TCM on some configurations. Poor contact here can cause unstable module operation.
• G110 — Located on the left (driver's) front lower side of the engine block.. This is a key grounding point for the engine block and is in the primary path for the main negative battery cable on many GMT900/K2XX trucks. Corrosion here directly impacts module power stability.
• TCM/TEHCM Connector — Inside the transmission oil pan, connected to the TEHCM which is mounted on the valve body (for 6L80/6L90 equipped models).. This connector provides all power, ground, and data signals to the TCM. Fluid intrusion or corrosion on these pins is a direct cause of TCM failure and related codes like P0604.
• Underhood Fuse Block (X50A) — On the driver's side of the engine compartment.. This fuse block contains the primary fuses for the ECM and TCM (e.g., 'TCM/ECM BATT' and 'TRANS IGN'). A loose fuse or corrosion in the block can cause intermittent power loss to the modules.

Real Owner Repair Stories

• Reddit user in r/MechanicAdvice (2009 Chevrolet Suburban (GMT900 platform)) — Persistent P0604 code that would not clear, even after multiple attempted fixes.
  ❌ Tried (didn't work) Replacing the ECM with a dealer remanufactured unit and flashing it, Removing an aftermarket CAN-bus connected radio, Testing all related fuses and relays, Checking all grounds and adding a missing hood ground strap
  ✅ What actually fixed it In a similar 2010 shop vehicle with a persistent P0604 after fixing other issues, the final solution was replacing the ECM a second time with a known-good used unit, which was then programmed. This suggests the first 'reman' ECM may have been faulty. The user confirmed all power and grounds to the ECM tested good before the final ECM swap.
• YouTube channel 'Pine Hollow Auto Diagnostics' (2010 Chevrolet Silverado (GMT900 platform)) — Check Engine Light with P0604 (Internal Control Module RAM error).
  ❌ Tried (didn't work) Initial diagnosis pointed towards a module issue after ruling out simple power/ground faults.
  ✅ What actually fixed it The problem was solved by replacing the Engine Control Module (PCM/ECM) and performing the necessary programming and relearn procedures (idle learn, crank learn) with a scan tool.

OEM Part Supersession History

• 24252363, 25798353, 24256670, 24257038 → 24256861, 19435614 — Internal revisions to improve reliability of the TEHCM assembly, addressing issues with pressure switches and solenoid performance.
  Heads up: While many part numbers for the 6L80 TEHCM have been superseded, it is critical to use a part number specified for the vehicle's VIN and calibration. Using an incompatible TEHCM can result in no-start conditions or failure to program.

Model Year Variations Within This Range

• 2008-2013 (GMT900): These models use a well-established electrical architecture. The 6L80E transmission with its internal TEHCM is the most common source of P0604 when it's not a power supply issue. Grounding locations and schemes are specific to this platform.
• 2014-2015 (K2XX): The K2XX platform introduced a new electrical architecture with different module communication protocols and wiring. While still using the 6L80E, the ECM and other modules are different. The 8-speed (8L90) transmission became available in late 2015, which uses an external TCM, making diagnosis and replacement different from the 6-speed's internal TEHCM.