Possible Causes
Rich fuel system condition can be caused by leaking fuel injectors, defective fuel pressure regulator, restricted or blocked fuel return line, leaking purge valve, defective purge solenoid, open or short in purge solenoid circuit or defective powertrain control module. To diagnose fuel system concerns, see BASIC FUEL SYSTEM CHECKS (A-7) in appropriate BASIC DIAGNOSTIC PROCEDURES article. To diagnose purge control system concerns, see EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
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Constantly monitored.
Coast down throttle angle offset greater than 5 degrees from learned value.
PCM will set Code P085 and turn on SERVICE ENGINE SOON light.
Note. Test number refers to number on diagnostic chart.
- If engine stalls, continue test. Stall may be caused by carbon deposits on throttle valves and in throttle bores.
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PCM Code P024 not set, engine running and vehicle speed greater than 30 MPH.
Vehicle speed cycles from 30 MPH or greater to zero MPH with no TCC brake switch input. PCM must record 10 of these events to set code.
PCM will set Code P090 and turn on SERVICE VEHICLE SOON message. PCM disables cruise control.
Note. Test numbers refer to numbers on diagnostic chart.
- Tests TCC brake switch input to PCM data parameter PI71. If input is working correctly, display will change from HI to LO to HI. If display remains on HI, check circuit No. 420 and TCC brake switch for short to voltage. If display remains on LO, check circuit No. 420 for an open or short to ground.
- Checks for voltage present at TCC brake switch connector terminal "A".
- Checks resistance between TCC brake switch terminal "A" and ground.
- Checks resistance between TCC brake switch terminal "B" and ground.
- Checks if TCC brake switch needs to be adjusted or replaced, or if PCM is faulty.
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Constantly monitored.
Any 4-digit code that does not match codes shown in chart for 64 seconds. Engine start while Code 1100 (Park) or Code 1010 (Neutral) not present. PCM commanding 4th gear although engine-to-vehicle speed indicating 4th gear achieved with Code 1100 (Park) or Code 1010 (Neutral).
PCM turns on SERVICE VEHICLE SOON message. PCM disables cruise control.
If all digits of PD71 and PD72 are 1, check for an intermittent loss of ground in park/neutral switch. If an intermittent PCM Code P091 occurs when gear selector lever is moved, code is most likely caused by a misadjusted shift linkage or park/neutral switch, causing park/neutral switch to end up in range between gears.
If code and SERVICE VEHICLE SOON message comes on while driving or when gear selector is not being moved, record PD71 and PD72 and compare values to chart. For example, if transmission was in OD when message came on and PD71 indicates 10 and PD72 indicates 11, check for intermittent open in circuit No. 773.
Manipulate related wiring and connectors while observing parameters PD71 and PD72 (or scan tester display). If an intermittent is induced, digit corresponding to that circuit will change. If wiring and connectors are okay, substitute a known good park/neutral switch, and recheck.
