Code
P1636
HUMMER
P — Powertrain
PCM Stack Overrun
AI status
Completed
Completed
100%
Causes
- Corrupted or buggy PCM software/calibration
- Failed or failing PCM (hardware fault)
- Intermittent or low supply voltage (battery/charging issues)
- Poor or corroded PCM power or ground connections
- Voltage spikes or transient electrical events
- Shorts or intermittent faults on CAN/data bus or sensor circuits causing unexpected interrupt loops
Symptoms
- MIL (Check Engine) lamp illuminated
- Multiple or sporadic, seemingly unrelated trouble codes
- Intermittent drivability issues, rough idle or stalling
- Hard/no-start conditions if PCM resets repeatedly
- Loss of communication with PCM on scan tool or intermittent module appearance
- Random module/component failures or disabled features
What to check
- Scan and record all stored and pending DTCs and freeze frame data; note occurrences and sequences
- Check for other module communication errors on network (CAN/BUS)
- Verify battery state of charge and charging system (resting voltage, cranking voltage, alternator output)
- Inspect PCM connectors and harness for corrosion, bent pins, water intrusion, or physical damage
- Check main power and ground circuit continuity and resistance to chassis/negative battery (low ohms expected)
- Look for recent repairs, aftermarket installations or attempted PCM reflashes
Signal parameters
- Battery/resting voltage: about 12.4–12.8 V (vehicle off); with engine running 13.5–14.8 V
- Cranking voltage: typically >9.5 V under starter load (spec varies by vehicle)
- PCM primary supply pin(s): should be battery voltage with ignition ON (near 12 V)
- PCM ground resistance to battery negative: typically
- CAN bus idle voltages: approx. 2.5 V on CAN_H and CAN_L relative to chassis (verify with manufacturer specs)
- Observe CAN differential activity during communication (presence of frames when bus active)
Diagnostic algorithm
- Read and document all DTCs, freeze frame data and event counters using a manufacturer-level scan tool.
- Check battery voltage and charging system; recharge or replace battery if low or weak. Re-test code presence after stable supply restored.
- Visually inspect PCM and connectors for damage, corrosion or moisture. Repair any harness damage and ensure secure connections.
- Verify power and ground circuits to PCM: measure voltage at PCM power pins with key ON and measure ground resistance to battery negative.
- Check the CAN/data bus for continuity, correct termination and proper idle voltages; isolate any shorted branches or noisy nodes.
- Check for recent reflash attempts or aftermarket modules. If a reflash failed or calibration mismatch suspected, obtain correct manufacturer flash file.
- If wiring and supply are good, attempt to clear codes and reflash/update PCM with latest OEM software per TSBs; perform reflash using approved procedure and stable power source.
- After reflash, clear codes and road test while monitoring for reappearance. If code returns and all wiring/power/communications are confirmed good, replace the PCM as a last resort.
- After PCM replacement, program module with vehicle-specific calibrations and perform relearns, then verify system operation and absence of return codes.
Likely causes
- Corrupted/incorrect PCM flash or interrupted reflash
- PCM hardware failure due to internal component fault or heat/water damage
- Low battery/unstable supply during module operation or programming
- Poor ground or power connector causing resets and stack corruption
- Communication bus faults (CAN) causing repeated exceptions in PCM software
Fault status
Status
PCM Stack Overrun — internal controller detected a stack/memory overflow or corruption; fault logged when module operation exceeded internal safe limits.
Repair difficulty: Hard
Diagnostic time: 2-6 hours
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Repair manuals
Manual library for HUMMER
138
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