Fault with the key or transponder, such as a worn, damaged or unprogrammed key; Poor connection, corrosion or wiring fault on the data line between the ECM and the theft deterrent or body control module; Low battery voltage or poor power and earth supply to the ECM or security module causing communication dropouts; Faulty immobiliser antenna or key reader (ring around the ignition barrel) or ignition switch fault; Replacement ECM or security module not correctly learned or matched to the vehicle; Internal fault in the ECM or theft deterrent module.

P1502

Theft Deterrent System No Password Received.

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
02: FaultThe specific fault in that area

What it means

On GM vehicles, P1502 means the engine control module (ECM/PCM) did not receive the expected security password from the theft deterrent system (such as the body control module or immobiliser module) when it was requested. Without a valid password exchange the ECM may restrict fuel or starting as an anti-theft measure. Exact module names and how the check is carried out vary by model and year.

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
Fuel injection or starter disabled
Other communication or security-related codes stored in several modules

Possible causes

Fault with the key or transponder, such as a worn, damaged or unprogrammed keylikely
Poor connection, corrosion or wiring fault on the data line between the ECM and the theft deterrent or body control modulelikely
Low battery voltage or poor power and earth supply to the ECM or security module causing communication dropoutspossible
Faulty immobiliser antenna or key reader (ring around the ignition barrel) or ignition switch faultpossible
Replacement ECM or security module not correctly learned or matched to the vehiclepossible
Internal fault in the ECM or theft deterrent modulerare

How to diagnose

Read all stored codes and freeze frame data from every module, noting any security or communication codes alongside P1502
Check battery condition and charging voltage, and make sure power and earth connections to the ECM and body control module are clean and secure
Try a second known-good, correctly programmed key to see whether the fault follows the key
Inspect the ignition barrel area, key reader and its wiring and connector for damage, moisture or corrosion
Inspect the security data circuit and connectors between the ECM and the theft deterrent module for chafing, corrosion or loose pins
Watch security status data on a scan tool while turning the ignition on to see whether the password exchange completes
Check whether the ECM or security module has recently been replaced or reflashed, and follow the manufacturer procedure for the model to confirm it has been learned correctly
Check the manufacturer's service information for the specific model, as the diagnostic procedure depends on the security system fitted

How to fix

Reprogram or replace the key or transponder as required
Repair or replace damaged wiring, connectors or terminals on the security data circuit
Restore good battery condition and repair any poor power or earth connections
Replace the faulty key reader, antenna or ignition switch
Carry out the manufacturer's security relearn or password synchronisation procedure for the ECM and security module
Replace and correctly program the ECM or theft deterrent module only after wiring and supply faults are ruled out

Can I keep driving?

Medium severity

If the car runs, it can usually be driven, but the fault may leave it unable to restart or cause it to stall, so get it diagnosed soon. If it will not start, it needs repair before it can be used.

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