Antitheft and Alarm Systems

Security System - Fuel Enable Circuit Diagram:

CIRCUIT DESCRIPTION:

When the ignition is turned "ON", the PASS-Key decoder "reads" the key resistor pellet. If the proper resistance is recognized by the PASS-key decoder module, it sends a PWM fuel enable signal via CKT 229 to the PCM. The PCM looks for this signal during cranking and allows fuel delivery by enabling the injectors when the signal is recognized. If the fuel enable signal is lost while the engine is running, the PCM will store code 58 and the vehicle will run normally. As long as code 58 is stored, the PCM will ignore any absence of the fuel enable signal and the car will start and run as long as the problem is isolated to the fuel enable circuit only.

TEST DESCRIPTION

Code 58 Diagnostic Chart:

Numbers below refer to circled numbers on the diagnostic chart.

1. If the vehicle will not crank with code 58 stored, the problem affects the entire PASS-key system and is not isolated to the fuel enable circuit.

2. The PCM supplies 5 volts to CKT 229 which the PASS-key decoder module pulses to ground when the correct key is recognized. This test ensures that the PCM is supplying 5 volts and CKT 229 is not open or shorted to ground.

3. Checks the PWM signal from the PASS-key module. Since the 5 volts supplied by the PCM is being pulsed to ground, voltage on CKT 229 should measure around 2.5 volts.

4. Checks for a faulty PCM or intermittent condition by clearing code 58. Since the PCM ignores the absence of a fuel enable signal only when 58 is stored, the vehicle should not start if the problem is present and code 58 is not.


DIAGNOSTIC AIDS:
An intermittent Code 58 and possible "no-start" condition could be caused by:

^ Loss of power or ground to PASS-key decoder module. A loose ground or poor ignition or battery connection.

^ Dirty, damaged, or loose connections or damaged harness. Check for any damage to the harness which could cause an intermittent open or short to ground, backed out terminals at the PCM and PASS-key decoder module connectors, broken locks, improperly formed or damaged terminals.