Diagnostic Aids

Perform this test only when directed by QUICK TEST. To prevent replacing good components, check following non-EEC areas for fault:

• Engine Base Condition (Cam Timing, Valves Rings, etc.)
• Electrical (Alternator, Battery, Add-On Devices, etc.)
• Transmission Shift Linkage

This test is not intended to diagnose transmission. Test diagnoses following items.

• Wiring Harness Circuits MLP, TSR, TSL, TSD, TSOD And SIG RTN
• ECA

Fig 1: Manual Lever Position (MLP) Sensor Circuit

1. 1) KOEO Codes 634, 522 & 654  KOEO Codes 634, 522 and 654 indicate MLP sensor is out of self-test range (3770-4607 ohms) when gear selector is in Park position. Following are possible causes of faults: Linkage Not Adjusted Correctly, Faulty Manual Lever Position (MLP) Sensor, Circuit Open Or Grounded or Faulty ECA.

   Turn ignition off. Apply parking brake. Place transmission gear selector in Neutral position. Place Manual Lever Position (MLP) sensor gauge in sensor slot. If gauge does not fit, loosen MLP mounting bolts, and adjust sensor as necessary. If gauge fits, go to step 2).

2. 2) Check MLP Sensor Circuit Continuity  Turn ignition off. Disconnect MLP sensor wiring harness connector. Disconnect 60-pin ECA connector. Inspect terminals and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Measure resistance between MLP terminal at MLP sensor wiring harness connector and test pin No. 30 at breakout box. Measure resistance between SIG RTN terminal at MLP sensor wiring harness connector and test pin No. 46 at breakout box. If either resistance is more than 5 ohms, repair open circuit and repeat QUICK TEST  . If each resistance is 5 ohms or less, go to step 3).
3. 3) Check MLP Sensor For Short To Power & Ground  Turn ignition off. Leave ECA and MLP sensor disconnected. Measure resistance between test pin No. 30 and test pins No. 40, 46 and 60 at breakout box. Measure resistance between test pin No. 30 and chassis ground. If resistance is less than 10 k/ohms, repair short circuit, and repeat QUICK TEST  . If resistance is 10 k/ohms or more, go to step 4).
4. 4) Check MLP Sensor Resistance  Turn ignition off. Connect MLP sensor. Leave ECA disconnected from breakout box. Measure resistance between test pins No. 30 and 46 at breakout box while cycling gear selector. See MLP SENSOR RESISTANCE table. If resistance is within specification, replace ECA, and repeat QUICK TEST  . If resistance is not within specification, replace MLP sensor, and repeat QUICK TEST.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 4) to step 7). No test procedures have been omitted.
5. 7) Incorrect Shift/No Shift  Turn ignition off. Check transmission fluid and add or replace if necessary. Test drive vehicle to determine transmission shift patterns. If transmission always remains in 3rd gear when vehicle is operated with shift lever in Drive or Overdrive position, go to step 8). If transmission does not operate as described, go to step 20).
6. 8) Visual Inspection  Visually check select switch and solenoid wiring harness between ECA and transmission. Repair or replace wiring harness as necessary. If wiring harness is okay, go to step 9).
7. 9) Diagnose Transmission Shift Patterns  If transmission upshifts and downshifts correctly, EEC-IV system is okay. Fault is in transmission. If transmission does not shift correctly, check harness and connectors for intermittent opens and shorts.
8. 10) Code 634  Code 634 indicates ECA has received incorrect voltage signals from gear select sensors. Clear continuous memory codes. Start engine. Shift gear selector to each position, leaving selector in each gear for 10 seconds. Turn ignition off. Shift gear selector to Park position. Perform KOEO SELF-TEST  . If Code 634 is not present, fault is intermittent. Go to step 20). If Code 634 is present, go to step 20).
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 10) to step 20). No test procedures have been omitted.
9. 20) Recheck For Code 634  Clear continuous memory codes. Turn ignition on. Shake and bend select switch wiring harness circuit between ECA and transmission. Shift gear selector through entire range and then place in Park position. Perform KOEO SELF-TEST  . If Code 634 is present, isolate fault and repair as necessary. If Code 634 is not present, go to step 21).
10. 21) Inspect Circuit  Turn ignition off. Inspect transmission switches and harness connectors for corrosion and damaged pins. Inspect wiring harness for incorrect routing. If any faults are found, repair or replace as necessary. If no faults are found, problem is intermittent and cannot be found at this time.