Diagnostic Aids

Enter this test only when all steps under QUICK TEST have been successfully completed and engine still does not start or if directed here from another test or chart. This test is only intended to diagnose:

AFCM (on Contour).
Compuvalve (on F-Series).
PCM.
SCP (+/-) communication link for open or short to ground.

NOTE: During bi-fuel diagnostics, intermittent failures are possible. Perform wiggle test and tap lightly on relays during testing. Ensure LPG fuel level is correct before continuing with diagnostics. F-Series models use a compuvalve and Contour models use an Alternate Fuel Control Module (AFCM).

1) Check AFCM PIDs

Perform PARAMETER IDENTIFICATION (PID)/DATA MONITOR PROCEDURE . Access the AFCM. Access an active PID. If communication is not possible with AFCM, go to next step. If communication is possible with AFCM, system is operating correctly at this time. See INTERMITTENT TESTS .

2) Check Signal Link For Open

Turn ignition switch to OFF position. Disconnect compuvalve harness connector C4025 and AFCM harness connector C4001. Check for continuity between specified compuvalve harness connector C4025 and AFCM harness connector C4001 terminals. See SIGNAL LINK OPEN CIRCUIT CHECK table. If continuity exists between specified terminals, go to next step. If continuity does not exist between specified terminals, repair open circuit between AFCM and compuvalve. See WIRING DIAGRAMS article.

SIGNAL LINK OPEN CIRCUIT CHECK ⁽¹⁾

Compuvalve Harness Connector Terminal No. (Wire Color)

AFCM Harness Connector Terminal No. (Wire Color)

54 (White)

13 (White)

56 (White)

12 (Violet)

58 (White)

14 (Orange)

60 (White)

4 (Light Green)

⁽¹⁾	Measure between specified terminals. For terminal locations, see Figure and Figure .

3) Check Shield Ground

Ensure ignition switch is turned to OFF position. Ensure AFCM harness connector C4001 is disconnected. Measure resistance between chassis ground and AFCM harness connector C4001 terminal No. 1 (Gray wire). If resistance is less than 5 ohms, replace AFCM, then go to next step. If resistance is 5 ohms or more, repair open in Gray wire between AFCM and G091. See WIRING DIAGRAMS article.

4) Check Compuvalve Communication

Perform PARAMETER IDENTIFICATION (PID)/DATA MONITOR PROCEDURE . Access the AFCM. Access an active PID. If communication is not possible with AFCM, replace compuvalve. If communication is possible with AFCM, system is operating correctly at this time.