Engine Speed Dips When Gear Is Engauged (Automatics)

ENGINE SPEED DIPS WHEN A GEAR IS SELECTED (AUTOMATICS)

Preconditions
^ DTCs absent.
^ Engine is hot.
^ Fault is permanent.

Fault Sources
^ Break in signal lead from AW 50-42 TCM.
^ Signal lead short circuited to ground or voltage supply.
^ Contact resistance in connectors.
^ Defective gear selector mechanism or Idle Air Control (IAC) Valve.

TESTING PROCEDURE





Checking the Signal From AW5O-42 TCM
^ START the engine and let it run at idling speed.
^ Move gear selector lever to N and note Scan Tool (ST) indication.
^ Move gear selector lever to D and note ST indication.





^ Compare the readings in the table to continue fault tracing.





Checking the IAC Valve's Connector
^ Clean and grease the ECM's and IAC valve's connector.
^ Check if engine speed still dips.

If engine speed still dips:
- Test with a new IAC valve.





Checking the Signal Lead, Constant P/N
^ Ignition OFF.
^ Wait for approx. 150 seconds.
^ Disconnect the TCM.
^ Connect the break-out box to the TCM wiring.
^ Ignition ON.





^ Connect a voltmeter between #29 (ECM A29) and #44 (ECM B14) on the break-out box.

If the value is 8 - 9 Volts:
- Check the signal from the gear selector lever to the TCM.
If the value is above 9 Volts:
- Check the lead between ECM B24 on the ECM and TCM B14 on the TCM for signs of short circuiting to voltage supply.
If the value is under 8 Volts:
- Check the lead between ECM B24 on the ECM and TCM B14 on the TCM for signs of a break.





Checking the Signal Lead, Constant R/D/3/L
^ Ignition OFF.
^ Wait for approx. 150 seconds.
^ Disconnect the TCM.
^ Connect the break-out box to the TCM wiring.
^ Ignition ON.





^ Connect a voltmeter between #29 (ECM A29) and #44 (ECM B14) on the break-out box.

If the value is 8 - 9 Volts:
- Check the signal from the gear selector lever to the TCM.
If the value is below 8 Volts:
- Check the lead between ECM B24 on the ECM and TCM B14 on the TCM with regard to short circuiting to ground.