P1503

What it means

On a Buick, P1503 means the engine control module received an incorrect password from the theft deterrent system (the body control or immobiliser side), so the security handshake failed. The engine control module expects a valid coded message before it allows the engine to keep running, and what it received did not match what it has stored. This often follows a module replacement, a failed communication or a fault in the key or transponder reading circuit.

Symptoms

• Engine cranks but does not start, or starts and stalls after a second or two
• Security or theft warning light on or flashing in the instrument cluster
• Intermittent no-start that comes and goes with no pattern
• Fuel injection or ignition appears disabled while the engine cranks
• Engine management light on with the code stored

Possible causes

• Engine control module and security system not matched, for example after a replacement or used module fitted without a security relearnlikely
• Faulty or unreadable key transponder, or a damaged keylikely
• Fault in the theft deterrent data line between the security module and engine control module, such as damaged wiring or a poor connectorpossible
• Low battery voltage or poor earths and power feeds causing communication dropouts during crankingpossible
• Faulty body control module, immobiliser module or key reader (steering column coil) component, depending on modelpossible
• Internal fault in the engine control module corrupting the stored passwordrare

How to diagnose

1. Read all stored codes and freeze frame data, and note whether other security or communication codes are present
2. Check battery condition and charging voltage, and make sure the battery is healthy before any further testing
3. Try every spare key and see whether the security light behaves differently, to rule out a faulty key
4. Inspect the wiring, connectors and earths for the engine control module, security module and key reader for damage, corrosion or water ingress
5. Check the security data line and feeds for continuity and shorts, following the wiring diagram for the specific model and year
6. Monitor the security status and password data in live data while attempting to start, to see which module is not responding
7. Check whether the engine control module or body control module has recently been replaced or reprogrammed, as a security relearn procedure may be required

How to fix

• Carry out the manufacturer's security or immobiliser relearn procedure so the engine control module and security system match
• Replace a faulty key or re-learn the transponder to the vehicle
• Repair damaged wiring, connectors or earths in the security data circuit
• Restore battery health and clean or tighten power and earth connections
• Replace a faulty key reader, security module or body control module, then program it to the vehicle
• Replace or reprogram the engine control module only once the wiring and other modules are confirmed good

Can I keep driving?

This code for other makes

• P1503BMWIdle Speed Control Valve Closing Solenoid Control Circuit Signal Low
• P1503CadillacTheft Deterrent System Password Incorrect
• P1503ChevroletTheft Deterrent System Password Incorrect
• P1503ChryslerTheft Deterrent System Password Incorrect
• P1503GMTheft Deterrent System Password Incorrect
• P1503GMCTheft Deterrent System Password Incorrect
• P1503OldsmobileTheft Deterrent System Password Incorrect
• P1503OtherAuxillary Speed Sensor Fault
• P1503SaturnTheft Deterrent System Password Incorrect
• P1503VolkswagenLoad Signal From Generator Range Performance

Nearby codes

• P1502BuickTheft Deterrent System No Password Received
• P1504BuickVehicle Speed Output Circuit