Diagnostic Aids

Perform this test only when directed by QUICK TEST. This test is intended to diagnose the following:

• TP sensor.
• Wiring harness circuits (PWR GND, SIG RTN, TP, VPWR and VREF).
• Powertrain Control Module (PCM).

Normal range of throttle angle measurement for TP sensor is 0-85 degrees. To pass QUICK TEST procedure, range of throttle rotation (in degrees) must be within 3 percent of specification.

To prevent replacement of good components, be aware, the following non-EEC related areas may be at fault:

• Idle speed.
• Binding throttle shaft or linkage.
• TP sensor not seated.

1) Check For Binding Throttle Plate  DTC P1120 indicates TP sensor closed throttle position is below range of 3.4 percent (.17 volt). Possible causes for this fault are:

• Damaged wiring harness or connectors.
• Open in VREF circuit.
• Faulty TP sensor.
• Faulty Powertrain Control Module (PCM).

Inspect TP sensor connector for damage or corrosion. Inspect wiring harness between TP sensor and PCM for damage or corrosion. Repair as necessary, and repeat QUICK TEST. If no mechanical problem is found, go to next step.

2) Check For Stuck TP Sensor  Turn ignition off. Connect scan tool to DLC. Access TP PID on scan tool. While observing TP PID, slowly move throttle through range from closed to wide open throttle. If TP PID indicates any sudden drops to below 0.49 volt, go to next step. If TP PID increase and decrease is gradual and smooth, go to step 20).

3) Check VREF Circuit Voltage  With TP sensor disconnected, turn ignition on. Measure voltage between VREF and SIG RTN terminals at TP sensor wiring harness connector. If voltage is 4-6 volts, go to next step. If voltage is not 4-6 volts, check VREF circuit for open or short. Repair as needed.

4) Check TP Circuit Resistance  Turn ignition off. Leave TP sensor disconnected. Disconnect PCM 104-pin connector. Inspect connector for damage and repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between test pin No. 89 (TP) and TP terminal of TP sensor wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in TP circuit.

5) Check TP Sensor Signal To PCM  Turn ignition off. Connect PCM to breakout box. Start engine and idle for 2 minutes. While slowly opening throttle, measure voltage between test pins No. 89 (TP) and 91 (SIG RTN) at breakout box. If at any time voltage enters 0.17-0.40 volt range, replace TP sensor.