P0603 on 2007-2009 Hummer H2: Keep Alive Memory (KAM) Error Causes and Fixes

What's Unique About the 2007-2009 Hummer H2

On the Hummer H2 and its GMT900 platform mates, P0603 is frequently a simple electrical issue rather than a computer failure. These trucks are known for having electrical accessories and aftermarket modifications (alarms, stereos, GPS trackers) that can cause parasitic battery drain, leading to the low voltage conditions that trigger this code. Additionally, GM issued technical bulletins for this era, including one for the 2008 H2, noting that P0603 can appear in the Transmission Control Module (TCM), highlighting the network-wide sensitivity to voltage drops. [Bulletin #PIP4653E] Corroded or loose ground straps, particularly the main engine-to-chassis grounds, 🎬 Watch: How to find and fix every ground wire on your truck. are another common point of failure on these trucks that can cause this code.

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
• Rough or unstable idle
• Hesitation during acceleration
• Harsh or erratic transmission shifting
• Reduced fuel economy
• Difficulty starting the engine or no-start condition
• Intermittent stalling
• Illuminated ABS or traction control light in some cases
• In many cases, no noticeable symptoms other than the light, especially after a battery change

Most Likely Causes

1. Weak or Failing Battery 🔴 High Probability → Shop Vehicle Battery H2s have numerous electronics and are often fitted with aftermarket accessories that can drain the battery over time, leading to low voltage. A battery voltage drop is the most common trigger for a P0603.
   How to confirm: Test the battery voltage with a multimeter. A healthy battery should read around 12.6 volts with the engine off and 13.7-14.7 volts when running. For a definitive test, have an auto parts store perform a load test.
   Typical fix: Replace the vehicle's battery. An AGM style battery is often recommended for these vehicles.
   Est. part cost: $175-$350
2. Loose or Corroded Battery Terminals/Cables 🔴 High Probability → Shop Vehicle Battery Corrosion is common on all vehicles and creates resistance, interrupting the stable voltage required by the PCM's Keep Alive Memory. The terminal clamps must be tight enough that they cannot be moved by hand.
   How to confirm: Visually inspect the battery terminals and cable ends for white or greenish crust (corrosion) and ensure the connections are tight. Follow the main ground cable to the chassis and ensure that connection is also clean and tight.
   Typical fix: Disconnect the battery (negative first) and clean the terminals and cable clamps with a wire brush and a baking soda/water solution. Reconnect securely (positive first) and apply a terminal protector spray.
   Est. part cost: $5-$15
3. Recent Battery Disconnect or Replacement 🟡 Medium Probability → Shop Vehicle Battery Any time the battery is disconnected for service, the KAM is wiped, which will set this code on the first drive cycle. This is considered normal behavior.
   How to confirm: If the battery was recently disconnected, jump-started, or replaced, this is the likely cause.
   Typical fix: Clear the code with an OBD-II scanner. If it doesn't return after several trips, no further action is needed.
   Est. part cost: $0
4. Aftermarket Accessories or Tuning 🟡 Medium Probability Improperly installed aftermarket alarms, stereos, or performance tuners can interfere with the PCM's power supply or communication, causing this code. This is a known issue on GM trucks and SUVs of this era. A voltage drop during the tuning process can also set the code.
   How to confirm: Check for any non-factory electronic devices. If a performance tuner was used, it may be the source. Disconnecting these devices one by one or performing a parasitic draw test may isolate the problem.
   Typical fix: Remove the interfering aftermarket device or have its wiring professionally corrected. If a tuner caused the issue, flashing the stock tune back to the PCM is necessary.
   Est. part cost: $0-$150

Rare But Worth Checking

• Failing Alternator: → Shop Alternator If the alternator isn't properly charging the battery, the resulting low or fluctuating system voltage can trigger a P0603 code. Check the charging system voltage with the engine running; it should be stable between 13.7 and 14.7 volts.
• Corroded/Loose PCM or Chassis Ground Connections: The H2, like other GMT900 trucks, relies on several key grounding points. There are ground posts under the driver's side dash and on the frame that can become loose or corroded, causing a host of intermittent electrical issues, including P0603. Inspecting and cleaning these grounds is a critical step before suspecting a bad module.
• Faulty Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) While possible, a bad PCM is the least likely cause. All other power and ground issues should be exhaustively ruled out before condemning the module. The provided TSBs also mention this code in relation to internal module faults, but diagnosis should always start with the power supply. [Bulletin #PIP4653E, Bulletin #05-06-04-060A]

Diagnosis Steps

1. Check for other codes: Use an OBD-II scanner to see if any other codes are present. Address those first, as they may be the root cause.
2. Inspect the Battery: Visually inspect the battery terminals for corrosion or loose connections. Clean and tighten as needed. The clamps should not move when twisted by hand.
3. Test Battery and Charging System: Use a multimeter to test the battery voltage (should be ~12.6V off, 13.7-14.7V running). A weak battery or failing alternator is a primary cause. Get a free load test at an auto parts store for confirmation.
4. Check Historical Context: Determine if the battery was recently replaced, disconnected, or jump-started. If so, clear the P0603 code and drive the vehicle. If the code does not return, the issue was a temporary power loss.
5. Inspect for Parasitic Draw: If the battery dies overnight, perform a parasitic draw test using a multimeter in-line with the negative battery cable. A draw over 50mA after 10 minutes is excessive. The draw should eventually stabilize below 20-30mA after all modules go to sleep (which can take up to two hours). Pull fuses one by one to isolate the circuit causing the drain. 🎬 See this step-by-step guide on performing a parasitic draw test. Common culprits on the H2 are aftermarket accessories, OnStar, and the radio.
🎬 Watch a mechanic diagnose and fix a real Hummer H2 battery drain.
6. Inspect Main Ground Connections: Check the primary ground points. Key locations include the negative battery cable-to-chassis connection (G100), the engine block-to-firewall strap (G104 to G108), and the main ECM ground on the engine block (G101/G103). Disassemble, clean, and securely retighten these connections.
7. Check for Aftermarket Devices: Inspect the vehicle for any aftermarket tuners, remote start systems, alarms, or stereos. These are common sources of electrical interference. Disconnect them to see if the code disappears.
8. Inspect PCM Power and Ground Wires: If the problem persists, check the wiring and connectors at the PCM for damage or corrosion. Verify the PCM is receiving constant battery voltage on its KAM circuit and has a solid ground connection using a voltage drop test (should be <0.5V).
9. Consider PCM Failure: If all power and ground circuits are confirmed to be good, the PCM itself may have an internal fault, though this is rare.

Parts You'll Likely Need

• Vehicle Battery (OEM #ACDelco Gold 48AGM (GM P/N 88864541) or 79PG are common fits.) — A weak or failing battery is the most frequent cause of the voltage drop that triggers a P0603 code.
  Trusted brands: ACDelco, DieHard, Optima
  OEM price range: $200-$350
  Aftermarket price range: $175-$300
• Battery Terminal Cleaner and Protector — Used to remove corrosion from battery posts and cable clamps, which restores a solid electrical connection.
  Trusted brands: CRC, Permatex, NOCO
  OEM price range: $5-$15
  Aftermarket price range: $5-$15
• Engine Ground Strap (OEM #e.g., GM 19434466) — The main engine-to-chassis ground can corrode or break, causing intermittent power loss to modules. This is a known issue on GMT900 trucks.
  Trusted brands: ACDelco, Dorman, Standard Motor Products
  OEM price range: $20-$40
  Aftermarket price range: $10-$25

Related Codes That Often Appear With This One

• P0601, P0604, P062F, P1621 — These are other internal control module memory or processor codes. GM Technical Service Bulletins group P0603 with these codes, indicating they can appear together when a module experiences an internal fault or power interruption. [Bulletin #PIP4653E, Bulletin #05-06-04-060A, 11]

Technical Service Bulletins (TSBs) & Recalls

• Bulletin #PIP4653E: Notes that DTC P0603 can be stored in the Transmission Control Module (TCM) along with other internal module codes, emphasizing that this is a system-wide voltage issue, not necessarily an engine computer fault.
• Bulletin #05-06-04-060A: An informational bulletin about various control module codes, including P0603, that can be shared across multiple modules. It advises technicians to identify which module set the code before diagnosis and notes that the final repair may be to replace the module if all other causes are ruled out.

Platform-Specific Known Issues

• The Hummer H2 is prone to parasitic battery drain from factory components like the OnStar module (if not updated or disconnected) and aftermarket accessories like alarms or stereos, which can lead to a weak battery and trigger a P0603 code.
• Multiple owners have traced complex electrical issues, including this code, to a communication breakdown at Splice Pack 205 (SP205), located behind the driver's side dash. This splice pack connects many of the vehicle's modules, and a fault in one module can disrupt the entire network.
• Corrosion of ground points is a common issue, especially in regions with high road salt use. There are critical ground posts under the driver's side dash and on the frame near the engine that require periodic inspection and cleaning.

Mechanic-Grade Diagnostic Values

• Parasitic Current Draw — expected: Should drop below 50 mA within 10 minutes of shutdown, and stabilize below 20-30 mA after all modules are fully asleep (up to 2 hours).. Failure: A sustained current draw above 50 mA indicates a component is not shutting down correctly and is draining the battery.
• ECM Keep Alive Memory (KAM) Power Pin Voltage — expected: Constant 12V+ (battery voltage) at the specific KAM power feed pin on the ECM connector, even with the key off.. Failure: Any voltage drop or a complete loss of voltage indicates a problem with the wiring or fuse supplying constant power to the ECM.
• ECM Power/Ground Circuit Voltage Drop — expected: Less than 0.5 Volts.. Failure: A reading greater than 0.5V on either the power side (testing between the connector pin and positive battery post) or ground side (testing between the ground pin and negative battery post) indicates excessive resistance in the circuit.

Scan Tool Commands That Help

• GM Tech 2 / GDS2 (or equivalent high-end scanner): Module Status / KAM Checksum Validation — After verifying power and grounds are good, this function can be used to ask the module to self-report the status of its internal memory. A checksum failure reported by the module itself points towards an internal PCM fault.

Wiring & Ground Locations

• ECM (Engine Control Module) — For the 2008 H2, the ECM is located below the battery and the underhood fuse block on the driver's side of the engine compartment.. This is the module setting the code. Its power and ground connections are critical. Proximity to the battery makes it susceptible to damage from battery leaks or fumes.
• G100 / G102 — The main battery ground cable connection to the left front frame rail and engine block.. This is the primary ground path for the entire vehicle's electrical system. Corrosion or a loose connection here can cause widespread issues, including P0603.
• G103 — Located on the front of the passenger side (right side) cylinder head.. This is a primary engine harness ground point. On some GM schematics, this ground is directly tied to the ECM/PCM.
• G104 & G108 — G104 is a ground strap on the left rear corner of the engine (driver's side). This strap connects to G108, which is located on the firewall in the driver's side rear corner of the engine bay.. This engine-to-body ground strap is crucial for providing a stable ground reference for all modules. Corrosion on the firewall at G108 is a common cause of intermittent electrical faults.
• Under-dash Grounds — A cluster of ground posts located under the driver's side dash, against the left side chassis wall, behind the kick panel.. These ground points service many interior modules, including the Body Control Module (BCM). A loose connection here can cause strange electrical behavior that may contribute to system voltage instability.

OEM Part Supersession History

• 12612384, 12617174, 12617568, 12617630 → 12622141, 12629001 — Standard hardware and software revisions by the manufacturer.
  Heads up: These part numbers are generally for the 2008 H2 with the 6.2L engine. They are not compatible with the 2007 model's 6.0L engine. The PCM must be programmed with the vehicle's VIN.
• 12625455 →
  Heads up: This is a common part number for the 2009 Hummer H2. It is not backward compatible with 2007 models.

Model Year Variations Within This Range

• 2007 vs. 2008-2009: The powertrain and its control module are different. The 2007 model with the 6.0L V8 uses a different PCM than the 2008-2009 models with the 6.2L V8 (E38 ECM). Part numbers are not interchangeable between these ranges.