Diagnostic Aid

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

1. 32)  Leave ignition off and STC disconnected. Connect DVOM between test pin No. 45 (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. 33)  Turn ignition off. Disconnect TP-B sensor wiring harness connector. Measure voltage between connector terminals SIG RTN and VREF. 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 .
   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. 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.

   Disconnect air tube from ST assembly. Check throttle linkage for binding or sticking. Repair if necessary. If throttle linkage is okay, go to next step.

4. 41)  Turn ignition off. 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. 42) Measure VREF At TP-B Sensor  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 .