Powertrain Controls - ECM/PCM

Overdrive Ratio Error Circuit:

Circuit Description:
The PCM/TCM monitors the difference in engine rpm and input shaft rpm. With transmission in "drive," the "Scan" tool reading should show engine speed closely matching input speed.

Overdrive Ratio Error Diagnostic Chart:

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Code 68 will set if:

^ Engine speed is 200 rpm higher than input speed.
^ 4th gear is indicated.
^ TCC is enabled.
^ All conditions are met for 2 seconds.
^ Not in park or neutral.

2. This test monitors signal sent to the PCM/TCM from the transmission.

3. This test confirms engine rpm signal to PCM/TCM.


Diagnostic Aids:
^ Check for deformed connectors at pass-thru connector.
^ Code 68 will set when going to default (2nd gear).
^ Refer to PCM/TCM intermittant codes.