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Diagnostic Aid

WARNING: This page is about a different car, the 1996 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.

On every power-up, the series throttle is commanded to self-test from the PCM. To verify this signal, go to next step.

  1. Step 32) Leave ignition off and STC disconnected. Connect DVOM between test pin No. 18 (TAPW) and 91 (SIG RTN) at the breakout box. While observing DVOM, turn ignition on. If DVOM indicates a brief change of voltage (2.0 volt minimum) as ignition is turned on, replace STC and repeat QUICK TEST . If DVOM does not indicate a brief change of voltage, replace PCM and repeat QUICK TEST .
  2. Step 33) Leave ignition on. Disconnect TP-B sensor wiring harness connector. Measure voltage between connector terminals SIG RTN (Gray/Red wire) and VREF (Brown/White wire). If voltage is 4-6 volts, replace TP-B and repeat QUICK TEST . If voltage is not 4-6 volts, see procedures under CIRCUIT TEST C.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 33) to step 40). No test procedures have been omitted.
  3. Step 40) DTC P1224: Check ST Assembly  This DTC should be disregarded if any other DTCs are present. DTC P1224 indicates TP-B voltage was out of range during self-test. Possible causes are as follows:
    • TP-B sensor binding or sticking.
    • Throttle stop screw misadjusted.
    • Faulty TP-B.
    • Faulty ST.

    Check throttle linkage for binding or sticking. Repair if necessary. If throttle linkage is okay, go to next step.

  4. Step 41) Turn ignition off. Disconnect air tube from ST assembly. Connect scan tester to Data Link Connector (DLC). Turn ignition on. Using scan tester, access TPB PID. While observing PID voltage, push throttle plate shut and then release. Throttle plate should not bind or stick. If TPB-PID is 0.3-0.9 volt at wide open throttle, go to next step. If TPB-PID is not 0.3-0.9 volt at wide open throttle, check ST stepper motor and TP-B for damage. If no damage is present, replace TP-B and repeat QUICK TEST .
  5. Step 42) Turn ignition off. Disconnect TP-B wiring harness connector. Inspect connector for damage and repair if necessary. Turn ignition on. Measure voltage between SIG RTN and VREF terminal of TP-B wiring harness connector. If voltage is 4-6 volts, replace TP-B and repeat QUICK TEST . If voltage is not 4-6 volts, go to CIRCUIT TEST C.
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