P0606 on 2007-2013 Chevrolet Avalanche: PCM Processor Fault Causes and Fixes

What's Unique About the 2007-2013 Chevrolet AVALANCHE

On the GMT900 platform, which includes the 2007-2013 Avalanche, a P0606 code doesn't always mean the PCM itself has failed. GM has issued technical service bulletins (notably TSB #17-NA-132) warning that issues like an open circuit for the camshaft position sensor can incorrectly cause the PCM to report an internal fault, often without setting a specific cam sensor code. Furthermore, corroded or broken engine ground straps are a very common culprit on these trucks; specifically the G104 ground on the rear of the driver's side cylinder head and the G103 ground on the front of the passenger's side cylinder head. These poor grounds cause voltage instability that the sensitive E38 ECM interprets as an internal failure.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light is on
• Vehicle enters 'Reduced Engine Power' mode
• Engine may stall unexpectedly or fail to start
• Erratic automatic transmission shifting
• ABS or StabiliTrak warning lights may illuminate
• Noticeable decrease in fuel economy
• Gauges on the instrument cluster may behave erratically or stop working

Most Likely Causes

1. Weak Battery or Poor Connections 🔴 High Probability The complex electronics on the GMT900 platform are sensitive to low voltage. A weak or failing battery, or corroded terminals, can cause unpredictable voltage drops during cranking or under load, triggering a P0606 code.
   How to confirm: Test the battery with a load tester, not just a multimeter. A battery can show 12.4V+ but still fail under load. Check battery terminals and the main cable connection points for corrosion or looseness.
   Typical fix: Clean the battery terminals and cable ends thoroughly. Charge or replace the battery if it fails a load test.
   Est. part cost: $120-$250
2. Faulty PCM Power or Ground Circuits 🔴 High Probability Ground straps on GMT900 trucks are notorious for corroding and breaking. The most common failure points causing P0606 are the G104 ground (a braided strap from the rear of the driver's side cylinder head to the firewall) and the G103 ground (on the front of the passenger's side cylinder head).
   How to confirm: Visually inspect and physically tug on the ground straps. Perform a voltage drop test on the ECM's power and ground circuits while the engine is running. A reading greater than 0.1-0.3 volts indicates excessive resistance and a bad connection.
   Typical fix: Remove, clean, and securely re-attach the ground connections. Replace any broken or severely corroded straps. The firewall-to-engine strap (G104/G108) is a frequent replacement item.
   Est. part cost: $10-$50
3. Internal PCM Failure 🟡 Medium Probability While often misdiagnosed, the ACDelco E38 PCM can fail internally due to age, heat cycles, or electrical shorts from other failing components.
   How to confirm: This is a diagnosis of exclusion. 🎬 See this guide on diagnosing ECM processor errors If all other possible causes (battery, grounds, wiring, related sensor circuits per TSBs) have been thoroughly tested and ruled out, the PCM is the likely culprit.
   Typical fix: Replace the PCM. The new module must be programmed by a dealer or a qualified shop with the correct tools (e.g., GM MDI with SPS subscription).
   Est. part cost: $300-$800

Rare But Worth Checking

• Faulty Camshaft Position Sensor Circuit: A critical issue for this platform is documented in GM TSB #17-NA-132. It warns that an open in the cam sensor circuit can cause a P0606 to set during cranking *instead* of the correct cam sensor code (like P0340), leading to an expensive misdiagnosis. This should be checked before condemning the PCM.
• Aftermarket Programming/Tuning: An improper or corrupted software flash from an aftermarket performance tuner can cause internal conflicts within the PCM's logic. This can happen if the wrong Operating System (OS) is flashed or if the tune itself is unstable, leading to a P0606 code, often called a 'death code' in the tuning community.
• Wiring Harness Damage: Check the wiring harness leading to the PCM for any signs of chafing, melting, or rodent damage. A short circuit in a 5-volt reference wire or sensor input can overload the PCM's processor and trigger a P0606. Sometimes an unrelated component, like an exhaust pipe vibrating against the chassis, can cause electrical noise that the ECU interprets as a fault.

Diagnosis Steps

1. Read all stored fault codes with an OBD-II scanner.
2. Perform a full battery and charging system test. The battery must pass a load test, not just a voltage check. Ensure voltage is above 12.4V engine off and between 13.7V and 14.7V engine running.
3. Thoroughly inspect and clean the battery cables, terminals, and main power/ground distribution points.
4. Inspect all main engine and chassis ground connections. Specifically locate, clean, and tighten G103 (front passenger cylinder head) and G104 (rear driver cylinder head to firewall). Perform a voltage drop test on these grounds; anything over 0.2V under load is a problem.
5. Following TSB #17-NA-132, inspect the camshaft position sensor and its wiring for opens, shorts, or damage before considering PCM replacement.
6. Visually inspect the wiring harness connected to the PCM for any signs of damage, chafing, or corrosion. Wiggle the connectors with the engine running to see if the fault can be triggered.
7. If the vehicle has an aftermarket tune, flash it back to the stock program to see if the code disappears.
8. Clear all diagnostic trouble codes and test drive the vehicle to see if P0606 returns.
9. If the code returns immediately and all other steps have been exhausted, the PCM is likely faulty and requires professional diagnosis and probable replacement.

Parts You'll Likely Need

• Engine Control Module (ECM/PCM) (OEM #12633238, 12612384, 19210738 (ACDelco E38, VIN specific, verify part #)) — This is the part that fails if the P0606 code is caused by an actual internal processor fault, after all other electrical issues have been ruled out.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $400-$800
  Aftermarket price range: $250-$500
• Battery — A weak or failing battery is a very common cause of this code due to voltage instability affecting the PCM.
  Trusted brands: ACDelco, DieHard, Interstate
  OEM price range: $200-$300
  Aftermarket price range: $120-$250
• Engine Ground Strap (Firewall to Engine) (OEM #19434466 (for G108)) — The G104/G108 ground strap from the driver's side cylinder head to the firewall is a known failure point on GMT900 trucks that directly causes electrical issues and P0606.
  Trusted brands: ACDelco, Standard Motor Products
  OEM price range: $20-$40
  Aftermarket price range: $10-$25

Related Codes That Often Appear With This One

• P0340/P0341 — These codes for the camshaft position sensor circuit may appear with P0606. However, a known issue on these trucks is that P0606 can appear *instead* of these codes, masking the true problem.
• P0562/P0563 — These codes indicate system voltage is too low or too high. Their presence strongly suggests the P0606 is being caused by a battery or charging system issue, not a failed PCM.
• P0641 — This code for 'Sensor Reference Voltage 'A' Circuit/Open' often appears with P0606 in forum discussions. It points towards a wiring or ground issue that affects the 5V reference circuit shared by multiple sensors, which can overload the PCM processor.

Technical Service Bulletins (TSBs) & Recalls

• 05-06-04-060A: An informational bulletin from GM that notes DTCs P0601, P0602, P0603, P0604, P0606, P062F, P06F3, and P1621 can be shared across multiple modules, highlighting the potential for network or communication issues.
• 17-NA-132: A critical bulletin warning technicians NOT to replace the Engine Control Module (ECM) for a P0606 code until the camshaft position sensor circuit has been thoroughly checked for an open. The bulletin states the P0606 can set *instead* of the correct cam sensor code, leading to misdiagnosis.
• PIE0545A: A preliminary information bulletin that mentions a software anomaly can cause P0606. It advises reprogramming the ECM with the latest software before replacement.

Platform-Specific Known Issues

• Real-World Owner Experience: Intermittent Stalling and P0606: A user on TahoeYukonForum.com with a 2007 Yukon XL experienced intermittent no-start conditions, 'Reduced Engine Power' messages, and a P0606 code. Other users in the thread immediately pointed to a weak battery or dirty battery cable connections, noting that a simple voltage test isn't enough and that the terminals must be disassembled and cleaned. This highlights how crucial a stable power supply is before suspecting the PCM.
• Real-World Owner Experience: Bad Ground Strap Fix: Numerous owners on forums and in repair videos for GMT900 trucks have successfully resolved a P0606 code by replacing the braided ground strap located at the back of the driver's side engine head (G104), which connects to the firewall. This strap is difficult to see and access, but it frequently corrodes and breaks, causing a host of electrical gremlins, including the

Mechanic-Grade Diagnostic Values

• ECM Ground Circuit Voltage Drop — expected: 0.1 Volts or less. Failure: A reading greater than 0.3V indicates unacceptable resistance in the ground circuit, often due to corrosion or a loose connection.
• Alternator Output Voltage (Engine Running) — expected: 13.5 - 14.5 Volts. Failure: Voltage below 13.5V or above 14.5V points to a fault in the charging system (alternator or voltage regulator) which can cause voltage instability and trigger a P0606.
• Battery State of Charge (Engine Off) — expected: 12.4 - 12.6 Volts. Failure: A reading below 12.0V indicates a discharged or failing battery. A drop of exactly 2.1V (e.g., from 12.6V to 10.5V) can indicate a dead cell.
• ECM Power Supply at Connector — expected: Should match battery voltage. Failure: If the voltage measured at the ECM power pins (e.g., X1 Pin 20) is lower than the voltage at the battery terminals, it indicates high resistance in the power supply wiring or a faulty fuse block connection.

Scan Tool Commands That Help

• GM Tech 2 / GDS2 / MDI: SPS (Service Programming System) — This is not a diagnostic command, but a required function used to flash the vehicle's VIN, security information (VATS), and correct operating system into a new or replacement ECM. Failure to perform this step will result in a no-start condition.
• Professional Scan Tool: Module Self-Test (Mode $06) — Can be used to request the ECM to run its internal self-diagnostics. Reviewing the results may provide more specific details about processor-specific failures, although it often just confirms the P0606 fault.

Wiring & Ground Locations

• G103 — On the front of the passenger side (right) cylinder head.. This is a primary engine and ECM ground. Corrosion or looseness at this stud can cause unstable voltage and reference signals for the ECM, triggering a false P0606.
• G104 — On the rear of the driver's side (left) cylinder head, typically a braided strap connecting to the firewall.. This is arguably the most notorious ground on GMT900 trucks for causing P0606. It provides the main ground path for the engine block to the chassis. It is difficult to see and often breaks or corrodes, leading to a host of electrical issues that the ECM interprets as an internal fault.
• G108 — On the firewall in the left rear corner of the engine compartment, serving as the attachment point for the ground strap from G104.. This is the chassis side of the critical G104 ground connection. This connection point must also be clean and tight for the ground path to be effective.
• ECM Connector X1, Pin 20 (RD/WH wire) — At the E38 ECM, which is typically located on the driver's side of the engine bay, near the firewall.. This is a main battery positive voltage feed to the ECM. A voltage drop test between this pin and the positive battery terminal can identify high resistance in the power supply circuit.
• ECM Connector X1, Pin 19 (PK wire) — At the E38 ECM, which is typically located on the driver's side of the engine bay, near the firewall.. This is the Ignition 1 Voltage feed, which tells the ECM the key is on. Verifying proper voltage at this pin is a key step in diagnosing power supply issues.

Real Owner Repair Stories

• GMTNation forum user 'DocBrown' (GMC Sierra (GMT900 platform, similar to Avalanche)) — No start ('click, click, click'), intermittent start after wiggling positive battery cable, eventually went into limp mode with code P0606.
  ❌ Tried (didn't work) Cleaning the badly corroded positive battery cable terminal.
  ✅ What actually fixed it The positive post on the old battery itself was physically loose, causing an unstable connection. Replacing the faulty battery with a new one resolved the starting issues, cleared the P0606 code, and stabilized the vehicle's voltmeter reading.

OEM Part Supersession History

• Multiple Service Numbers → Varies by VIN — The ACDelco E38 ECM used in this generation has several service part numbers (e.g., 12597121, 12612384, 12625455, 12633238) that may have been used over the production run.
  Heads up: These are not always directly interchangeable without proper verification and programming. A replacement ECM must be compatible with the vehicle's specific VIN and options. It must be programmed with the latest GM operating system using the SPS (Service Programming System) to function. Simply installing a used module from another truck will result in a no-start condition due to a VIN and VATS (anti-theft) mismatch.

Model Year Variations Within This Range

• 2010-2012: The E38 ECM with service number 12633238 is noted by some vendors as being specifically for 2010-2012 GM trucks and SUVs. While the overall architecture is the same, this may indicate minor hardware revisions or software requirements that differ from earlier (2007-2009) or later (2013) models in the same generation.