91 Explorer overdrive malfunction
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91 Explorer overdrive malfunction
I have a 91 Explorer, 4wd, 4 door, eddie bauer. I recently had the A/C hoses replaced and when I got it back the overdrive would not engage. All of the other gears work fine, it just won't even attempt to shift to overdrive. Any suggestions?
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Joined: Dec 2001
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From: UT
3-4 shift is electronically controlled on the A4LD. 1st thing I'd do is verify EEC-IV control of the 3-4 shift.
Out of curiosity, is the torque converter lockup clutch (TCC) engaging in 3rd gear? The 3-4 shift solenoid shares power supply with the TCC lockup solenoid.
1st step: Get a wiring diagram so you can reference how it's wired in. Basic circuit is EEC relay supplies power to 3-4 shift solenoid, TCC lockup solenoid, and other things --> solenoid --> return wire to PCM --> PCM acts as ground side switch to control 3-4 shift.
2nd step: Run EEC-IV self-tests and make sure you get all pass codes. Engine management faults can cause the PCM to choose not to shift into 4th gear or engage TCC.
3rd step: If EEC-IV tests all pass, and problem persists, then verify the integrity of the 3-4 shift circuit. 12 V power at transmission? continuity through solenoid? solenoid to PCM wire ok? PCM ground ok?
4th step: If circuit checks ok, and problem persists, then perform EEC-IV output state test while monitoring voltage drop across suspect solenoid. This tests the ability of the PCM to tell the transmission to upshift to 4th gear.
5th step: If output state test is positive, then verify the PCM is "choosing" to tell the transmission to shift into 4th gear by performing a road test. While monitoring voltage drop across suspect solenoid and with vehicle at normal operating temperature, drive at 40 mph (50 if testing TCC solenoid). If the electrical state of the solenoid changes, then the PCM is telling the transmission to upshift.
If the transmission passes all of these tests, then the fault most likely lies inside the transmission -- either a hydraulic or mechanical fault
I've written this assuming the OD malfunction refers to 4th gear. Many people confuse OD (aka 4th gear) with the TCC lockup. Diagnosis of the TCC lockup electrical control circuit is essentially the same as for the 3-4 shift circuit.
Out of curiosity, is the torque converter lockup clutch (TCC) engaging in 3rd gear? The 3-4 shift solenoid shares power supply with the TCC lockup solenoid.
1st step: Get a wiring diagram so you can reference how it's wired in. Basic circuit is EEC relay supplies power to 3-4 shift solenoid, TCC lockup solenoid, and other things --> solenoid --> return wire to PCM --> PCM acts as ground side switch to control 3-4 shift.
2nd step: Run EEC-IV self-tests and make sure you get all pass codes. Engine management faults can cause the PCM to choose not to shift into 4th gear or engage TCC.
3rd step: If EEC-IV tests all pass, and problem persists, then verify the integrity of the 3-4 shift circuit. 12 V power at transmission? continuity through solenoid? solenoid to PCM wire ok? PCM ground ok?
4th step: If circuit checks ok, and problem persists, then perform EEC-IV output state test while monitoring voltage drop across suspect solenoid. This tests the ability of the PCM to tell the transmission to upshift to 4th gear.
5th step: If output state test is positive, then verify the PCM is "choosing" to tell the transmission to shift into 4th gear by performing a road test. While monitoring voltage drop across suspect solenoid and with vehicle at normal operating temperature, drive at 40 mph (50 if testing TCC solenoid). If the electrical state of the solenoid changes, then the PCM is telling the transmission to upshift.
If the transmission passes all of these tests, then the fault most likely lies inside the transmission -- either a hydraulic or mechanical fault
I've written this assuming the OD malfunction refers to 4th gear. Many people confuse OD (aka 4th gear) with the TCC lockup. Diagnosis of the TCC lockup electrical control circuit is essentially the same as for the 3-4 shift circuit.
