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P1503

Theft Deterrent System Password Incorrect.

  • GM
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
5
AreaVehicle speed, idle control and auxiliary inputs
03
FaultThe specific fault in that area

What it means

On GM vehicles P1503 means the Theft Deterrent System Password Incorrect. The engine control module (ECM/PCM) expects a valid security password or code from the body or immobiliser module, and what it received did not match or did not arrive. The engine may then start and stall, or refuse to start, as an anti-theft measure.

Symptoms

  • Engine cranks but does not start
  • Engine starts then stalls after a second or two
  • Security or anti-theft warning light on or flashing
  • No fuel or no injector pulse while cranking
  • Fault returns after a battery disconnect or module replacement

Possible causes

  • Engine control module and body/immobiliser module not matched (security link not learned) after replacement or reprogramminglikely
  • Ignition key transponder fault, damaged key or unprogrammed keylikely
  • Fault in the transponder reader or antenna ring around the ignition lock, or its wiringpossible
  • Wiring or connector fault on the security data line between modulespossible
  • Low battery voltage or poor earths causing corrupted communication between modulespossible
  • Faulty body control or immobiliser modulerare
  • Faulty engine control modulerare

How to diagnose

  1. Read all stored codes and freeze frame data, and note any other security or communication codes in the body or immobiliser module
  2. Check battery condition and charging voltage, and clean and tighten battery terminals and main earths
  3. Try a second known-good, correctly programmed key and inspect the original key for damage; see whether the security light behaves differently
  4. Check whether the security lamp status and the live data for security or fuel-disable status change with each key
  5. Inspect the ignition lock transponder reader, its connector and the wiring for damage, corrosion or water ingress
  6. Check the security data line and related module connectors for continuity, chafing and poor pin tension, following the wiring diagram for the model
  7. Check whether any module has recently been replaced or reprogrammed, as the procedure for relearning security varies by model and year

How to fix

  • Carry out the manufacturer's security or password relearn procedure so the modules are matched; the exact method depends on the model and year
  • Programme or replace the ignition key if the transponder is faulty or not learned
  • Repair or replace the transponder reader or antenna ring and its wiring
  • Repair damaged wiring or connectors on the security data line
  • Recharge or replace a weak battery and repair poor earth connections
  • Replace and programme a confirmed faulty body/immobiliser module or engine control module

Can I keep driving?

Medium severity

If the car starts and runs normally it can be driven, but it may fail to restart later, so have it fixed soon. If it stalls or will not start, it should not be driven until the security fault is fixed.

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

This code for other makes

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