P1631high severityPowertrain
Theft Deterrent Start Enable Signal Not Correct
on 1998 Buick Century 3.1L V6 · FWD
What this code means
The PCM received a start enable signal from the theft deterrent system, but the signal is not the expected value or pattern.
Symptoms
- Vehicle will not start
- Security light flashing
- Engine cranks but does not fire
Common causes
- Faulty key transponder
- Passlock sensor sending incorrect signal
- BCM internal fault
- Wiring issue corrupting signal
Diagnostic steps
- Test theft deterrent signal at PCM
- Check key transponder
- Test Passlock sensor output
- Inspect wiring
- Attempt security relearn
Repair notes
Perform security relearn. Replace Passlock sensor or BCM if signal remains incorrect.
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