DTC 85

Undefined Ratio Circuit:

Circuit Description:
The PCM/TCM calculates the actual gear ratio from input and output speed readings while in each gear, then compares these to what the gear ratio should be, taking into consideration the selected gear range. This monitor includes reverse but does not include overdrive.

Undefined Ratio Diagnostic Chart:

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

1. This test verifies the proper function of the input sensor.

2. Test two verifies the correct functioning of the output sensor.

Diagnostic Aids:
The PCM/TCM relies on the PSM to indicate what gear range has been selected, so the PSM must be functioning properly or Code 85 may be set.

Check all connections, especially those at the transmission pass-thru connector.

Gear Ratio Chart:

Compare "Scan" tool gear ratio reading to chart below.