Faulty or worn ignition key, or damaged key transponder or contact in the key; Fault in the ignition switch, lock cylinder or the key reader or sensing circuit; Damaged wiring, poor connections or corrosion in the cranking signal or security circuit; Low battery voltage or poor earths causing signals to drop out during cranking; Fault in the body control or theft deterrent module, or a communication fault between it and the PCM; Faulty PCM or a security learn or relearn procedure not completed after a repair.

P1629

Theft Deterrent System Cranking Signal.

Saturn
Powertrain
Manufacturer code
Medium severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
6: AreaComputer and output circuits
29: FaultThe specific fault in that area

What it means

P1629 on a Saturn means a fault in the Theft Deterrent System Cranking Signal. The powertrain control module (PCM) expects a valid cranking or start-enable signal linked to the vehicle theft deterrent system while the engine is being started, and it did not receive the expected signal or message. This can stop the engine starting or allow it to crank but not run, depending on the model and the security system fitted.

Symptoms

Engine cranks but will not start
Engine starts then stalls after a second or two
No crank in some cases
Security or theft deterrent warning light on or flashing
Intermittent starting problems that come and go
Check engine light on

Possible causes

Faulty or worn ignition key, or damaged key transponder or contact in the keylikely
Fault in the ignition switch, lock cylinder or the key reader or sensing circuitlikely
Damaged wiring, poor connections or corrosion in the cranking signal or security circuitpossible
Low battery voltage or poor earths causing signals to drop out during crankingpossible
Fault in the body control or theft deterrent module, or a communication fault between it and the PCMpossible
Faulty PCM or a security learn or relearn procedure not completed after a repairrare

How to diagnose

Read all stored and pending codes and freeze frame data, noting any other security, starter or communication codes
Check battery condition and voltage during cranking, and inspect battery terminals and earth connections
Try a spare key if available and inspect the key for damage, noting whether the security light behaves differently
Watch the security light when the ignition is turned on to see whether the system is recognising the key
Inspect the wiring and connectors at the ignition switch, the theft deterrent module and the PCM for damage, corrosion or water ingress
Using the wiring diagram for the specific model and year, check the cranking signal circuit for continuity, shorts and correct voltage during cranking
Check live data for security or start-enable status, if the scan tool supports it for this vehicle
Check whether the vehicle needs a security relearn procedure and what the manufacturer procedure is for your model

How to fix

Replace or reprogramme a faulty key, or use a known good key
Repair or replace the ignition switch or key reader if it is faulty
Repair damaged wiring or connectors in the cranking signal or security circuit
Charge or replace the battery and clean or repair poor power and earth connections
Replace the faulty theft deterrent or body control module and carry out the required security learn procedure
Replace or reprogramme the PCM only after the other causes are ruled out, then complete the security relearn

Can I keep driving?

Medium severity

If the car starts and runs normally, it can be driven carefully but get it checked soon, as it may fail to restart and leave you stranded. If it stalls or will not start, do not rely on it for journeys.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.