Code
P1621
OLDSMOBILE
P — Powertrain
PCM Memory Performance
Views:
UK: 38
EN: 70
RU: 37
AI status
Completed
Completed
100%
Causes
- Corrupted PCM software or internal memory (EEPROM/KAM) failure
- Low or intermittent battery voltage / poor charging system
- Bad power or ground connections to the PCM
- Water intrusion or corrosion at PCM connector or housing
- Failed PCM hardware
- Failed or interrupted PCM reprogramming/flash
Symptoms
- Malfunction Indicator Lamp (MIL) or Service Engine Light on
- Driveability issues: rough idle, stalling, reduced performance
- Intermittent or no communication with scan tool
- Vehicle may enter limp mode or refuse to start in severe cases
- Loss of learned values (idle adapt, fuel trims) after key cycle
What to check
- Scan for stored/related DTCs and record freeze frame data
- Verify battery voltage and charging system (crank and key ON voltages)
- Visually inspect PCM connector and harness for corrosion, damaged pins, or water
- Check PCM power and ground circuits for proper voltage and low resistance to battery
- Attempt communication with PCM using a scan tool; note any comm errors
- Check for Technical Service Bulletins (TSBs) and recent reflash history
Signal parameters
- Battery voltage (key ON, engine OFF and cranking voltage)
- PCM supply and ignition-switched feed voltages
- PCM ground circuit resistance to battery negative
- Module communication status (CAN/J1850/serial) and error counters
- Presence/consistency of KAM/EEPROM checksum or status flags (if supported)
- Engine rpm, throttle position, coolant temperature from freeze frame (for correlation)
Diagnostic algorithm
- Retrieve and record all stored DTCs and freeze frame data. Note any related P06xx or communication codes.
- Verify battery state-of-charge and charging system. Recharge or replace battery if low and retest.
- Visually inspect PCM connectors and wiring for corrosion, bent pins, damaged insulation, or signs of water intrusion. Repair any damage.
- With a wiring diagram, backprobe and verify PCM constant and switched power pins have proper voltage and verify primary ground circuits have low resistance to battery negative.
- Check for intermittent faults by wiggling harness at PCM and repeating communication/volt checks while monitoring scan tool for dropout.
- If wiring and power/ground are good, attempt a controlled reflash of PCM software per manufacturer procedure (use correct calibrations and stable battery/charger). Follow all programming precautions.
- If reflash is unsuccessful or code persists after successful reprogramming, consider replacing the PCM. Program and configure a replacement PCM per factory procedure and perform relearn procedures as required.
- After repair or replacement, clear codes and confirm drive-cycle testing until code does not return. If the code returns, escalate to advanced testing or factory support.
Likely causes
- Open/short/poor battery or ignition power feed to PCM
- Poor ground(s) at PCM chassis/engine grounds
- Internal PCM EEPROM or KAM (keep-alive memory) failure
- Connector corrosion, bent pins, or water damage
- Recent unsuccessful ECM/PCM reflash or aftermarket device interference
Fault status
Status
PCM memory/performance fault: internal memory error, checksum or KAM failure, or memory access problem.
Repair difficulty: Hard
Diagnostic time: 1.0-3.0 hours
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