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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:

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.
NOTE: HO2S11 (right) and HO2S21 (left) refer to upstream Heated Oxygen Sensors (HO2S).

  1. 1) Access PCM PIDs

    Warm engine to normal operating temperature. Connect New Generation Star (NGS) scan tool to Data Link Connector (DLC). Turn ignition switch to ON position (engine off). Using scan tool, access PCM HO2S11 or HO2S21 PID. Start engine and observe HO2S PIDs. HO2S PIDs should switch between 0 and 0.9 volt. If HO2S PIDs are within specification, go to next step. If HO2S PIDs are not within specification, go to step  10) for Contour, or step  3) for all other models.

  2. 2) Access AFCM PIDs

    Ensure engine is at normal operating temperature. Using scan tool, access AFCM HO2S11 or HO2S21 PID. Start engine and observe HO2S PID. HO2S PIDs should switch between 0 and 0.9 volt. If HO2S PIDs are within specification, replace compuvalve. If HO2S PIDs are not within specification, go to step  10) for Contour, or step  3) for all other models.

  3. 3) Check HO2S Circuits For Short To Ground

    Turn ignition switch to OFF position. Disconnect in-line harness connector C4037, PCM harness connector, and HO2S11 and HO2S21 connector. Measure resistance between chassis ground and in-line harness connector C4037 terminals No. 9 (Red/Black wire) and 10 (Gray/Light Blue wire). See Figure. If both resistance measurements are 10 k/ohms or more, go to next step. If either resistance measurement is 10 k/ohms or less, repair short to ground in affected circuit. See WIRING DIAGRAMS article.

  4. Check HO2S Circuits For Open

    Ensure ignition switch is turned to OFF position. Ensure in-line harness connector C4037, PCM harness connector, and HO2S11 and HO2S21 connector are disconnected. Measure resistance between specified in-line harness connector C4037 terminal and specified PCM harness connector terminal. See PCM-TO-CONNECTOR C4037 HARNESS OPEN CIRCUIT CHECK  table. If both resistance measurements are less than 5 ohms, go to next step. If either resistance measurement is 5 ohms or more, repair open in affected circuit. See WIRING DIAGRAMS article.
    PCM-TO-CONNECTOR C4037 HARNESS OPEN CIRCUIT CHECK (1)

    In-Line Harness Female Connector C4037 Terminal No. (Wire Color) PCM Harness Connector Terminal No. (Wire Color)
    9 (Red/Black) 87 (Red/Black)
    10 (Gray/Light Blue) 60 (Gray/Light Blue)
    (1) For connector terminal locations, see Figure and Figure .

  5. 4) Check Signal Return (SIGRTN) Circuit Between PCM & C4037 For Open

    Ensure in-line harness connector C4037, HO2S11 and HO2S21 connectors and PCM connectors are disconnected. Measure SIGRTN circuit resistance between in-line harness connector C4037 terminal No. 8 (Gray/Red wire) and PCM harness connector terminal No. 91 (Grey/Red wire). See Figure and Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Gray/Red wire between in-line harness connector C4037 and PCM. See WIRING DIAGRAMS article.

  6. Check Signal Return (SIGRTN) Circuit Between Both HO2S & C4037 For Open

    Measure SIGRTN circuit resistance between HO2S11 and HO2S21 harness connectors terminal No. 3 (Gray/Red wire) and in-line harness female connector C4037 terminal No. 8 (Gray/Red wire). See Figure and Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Gray/Red wire between in-line harness connector C4037 and HO2S11 or HO2S21. See WIRING DIAGRAMS article.

  7. 5) Check HO2S Circuit For Open

    Ensure in-line harness connector C4037, HO2S11 and HO2S21 connectors and PCM connectors are disconnected. Measure resistance between HO2S harness connector terminal No. 4 and in-line harness female connector C4037 terminals. See HO2S-TO-CONNECTOR C4037 HARNESS OPEN CIRCUIT CHECK  table. If both resistance measurement is less than 5 ohms, go to next step. If either resistance measurement is 5 ohms or more, repair open in affected circuit. See WIRING DIAGRAMS article.
    HO2S-TO-CONNECTOR C4037 HARNESS OPEN CIRCUIT CHECK (1)

    HO2S Harness Connector Terminal No. 4 (Wire Color) In-Line Harness Female Connector C4037 Terminal No. (Wire Color)
    HO2S11 (Gray/Light Blue) 10 (Gray/Light Blue)
    HO2S21 (Red/Black) 9 (Red/Black)
    (1) For connector terminal locations, see Figure and Figure .

  8. 6) Check Compuvalve Harness For Short To Ground

    Ensure in-line harness connector C4037 is disconnected. Disconnect compuvalve harness connector C4025. Measure resistance between chassis ground and compuvalve harness connector C4025 terminals No. 10 (White wire) and 30 (White wire). If both resistance measurements are more than 10 k/ohms, go to next step. If either resistance measurement is 10 k/ohms or less, repair short to ground in affected wire between harness connector C4037 and compuvalve. See WIRING DIAGRAMS article.

  9. Check Compuvalve Harness For Open

    Measure resistance between specified compuvalve harness connector C4025 terminals and in-line harness male connector C4037 terminals. See COMPUVALVE HARNESS OPEN CIRCUIT CHECK - EXCEPT CONTOUR  table. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, replace main harness to compuvalve.
    COMPUVALVE HARNESS OPEN CIRCUIT CHECK - EXCEPT CONTOUR (1)

    Compuvalve Harness Connector Terminal No. (Wire Color) In-Line Harness Male Connector C4037 Terminal No. (Wire Color)
    10 (White) 9 (White)
    30 (White) 10 (White)
    (1) For connector terminal locations, see Figure and Figure .

  10. 7) Check SIGRTN Circuit For Open

    Ensure compuvalve harness connector C4025 and in-line harness connector C4037 are disconnected. Measure resistance between compuvalve harness connector C4025 terminal No. 32 (White wire) and in-line harness connector C4037 terminal No. 8 (white wire). See Figure and Figure . If resistance is 5 ohms or more, replace main harness to compuvalve. If resistance is less than 5 ohms, check HO2S. See HEATED OXYGEN SENSOR (HO2S) under SENSORS under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - EEC-V (GASOLINE) article.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 7) to step 10). No test procedures have been omitted.

  11. 10) Check HO2S Circuits For Short To Ground

    Turn ignition switch to OFF position. Disconnect in-line harness connector C4037 and PCM harness connector. Measure resistance between chassis ground and in-line harness connector C4037 terminal No. 10 (White wire). See Figure. If resistance is 10 k/ohms or more, go to next step. If resistance is 10 k/ohms or less, repair short to ground in White wire between PCM and in-line harness connector C4037. See WIRING DIAGRAMS article.

  12. Check HO2S Circuits For Open

    Ensure ignition switch is turned to OFF position. Ensure in-line harness connector C4037 and PCM harness connector C4025 are disconnected. Measure resistance between in-line harness connector C4037 terminal No. 10 (White wire) and PCM harness connector C4025 terminal No. 60 (White wire). See Figure and Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in White wire between PCM and in-line harness connector C4037. See WIRING DIAGRAMS article.

  13. 11) Check Signal Return (SIGRTN) Circuit For Open

    Ensure in-line harness connector C4037 and PCM are disconnected. Disconnect HO2S11 harness connector. Measure resistance between PCM harness connector C4025 terminal No. 91 (Brown wire) and in-line harness connector C4037 terminal No. 8 (Brown wire). See Figure and Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Brown wire between PCM and in-line harness connector C4037. See WIRING DIAGRAMS article.

  14. 12) Check HO2S & Signal Return (SIGRTN) Circuits To HO2S11

    Disconnect HO2S11 harness connector C934 and in-line harness connector C4158. Measure resistance between C4158 terminal No. 4 (Brown wire) and HO2S11 harness connector C934 terminal No. 4 (Brown wire). Also, measure resistance between C4158 terminal No. 3 (White wire) and HO2S11 harness connector C934 terminal No. 3 (White wire). See Figure and Figure . If both resistance measurements are less than 5 ohms, go to next step. If either resistance measurement is 5 ohms or more, repair open in affected circuit. See WIRING DIAGRAMS article.

  15. 13) Check Compuvalve Harness For Short To Ground

    Ensure in-line harness connector C4037 is disconnected. Disconnect compuvalve harness connector C4025. Measure resistance between chassis ground and compuvalve C4025 harness connector terminals No. 30 and 32 (White wires). If both resistance measurements are more than 10 k/ohms, go to next step. If either resistance measurement is 10 k/ohms or less, replace main harness to compuvalve. See WIRING DIAGRAMS article.

  16. Check Compuvalve Harness For Open

    Measure resistance between specified compuvalve harness connector C4025 terminals and in-line harness male connector C4037 terminals. See COMPUVALVE HARNESS OPEN CIRCUIT CHECK - CONTOUR  table. If resistance is less than 5 ohms, replace compuvalve. If resistance is 5 ohms or more, replace main harness to compuvalve.
    COMPUVALVE HARNESS OPEN CIRCUIT CHECK - CONTOUR (1)

    Compuvalve Harness Connector Terminal No. (Wire Color) In-Line Harness Male Connector C4037 Terminal No. (Wire Color)
    30 (White) 10 (White)
    32 (White) 8 (White)
    (1) For connector terminal locations, see Figure and Figure .
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