Powertrain Controls - ECM/PCM

Low Ratio Error:

Low Ratio Error Circuit:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) calculates ratio based on the transmission input speed and output speed sensor readings. The PCM compares the known transmission ratio to the calculated ratio, for the particular gear range selected.

DIAGNOSTIC TROUBLE CODE (DTC) 86 WILL SET WHEN
- No DTC(s) 21, 22, 24, 28, 71, 72 and 74.
- Not in P,R,N.
- Engine speed greater than 300 RPM.
- TP greater than 25%.
- Vehicle speed greater than 7 mph.
- Trans gear ratio is less than 1.06 in first or second gear.
- All conditions met for 2 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
- 2nd gear.
- Line pressure set to maximum.
- Inhibit TCC operation.

DTC 86 WILL CLEAR WHEN
The fault no longer exists, and the ignition switch is cycled "OFF" then "ON."

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. An out of range trans range pressure switch could falsely indicate the actual transmission range.
2. This test compares the known ratio for a commanded gear to the calculated ratio displayed on the scan tool.

DIAGNOSTIC AIDS
This DTC will set when trans commanded gear is 1 or 2 and trans is mechanically in 3rd or 4th gear. DTC 81 is used to detect a 2-3 shift solenoid circuit malfunction.