Transmission Controls With PCM

Diagnostic Chart:

NO 1ST GEAR
During normal driving modes the PCM/TC adapts line pressure to prevent clutch slip and harsh shifts. If 1st clutch is slipping after pressure is adjusted to high line, it is determined that there is no 1st gear. First gear clutch is fed directly from the manual valve and is always applied in all forward gear selections.

DTC PARAMETERS
DTC 16 will set when the PCM has detected the following twice in an ignition cycle.
^ Vehicle speed is greater than 5 km/h (3 mph).
^ Turbine speed is greater than 224 rpm.
^ No turbine or vehicle speed signal noise.
^ High line pressure has been commanded.
^ Ratio failure counter equals 255 for an in-gear failure or the shift failure counter is greater than 100 on a downshift to 1st during acceleration (128 = 0 or normal operation).
Or
Second gear must be commanded on for the vehicle to move.

TEST DESCRIPTION
Numbered steps below refer to numbered steps on chart.
1. Check for DTC/information flag 14. It must be eliminated first as a possible cause for DTC 16 - No 1st gear.
2. Pressure test at the same temperature that fault occurred to assure the fault is not a pressure problem that only occurs in a particular temperature range. Low line pressure which would be indicated by DTC/information flag 14 line pressure low must be eliminated first as possible cause for DTC 16 - No 1st Gear.
3. Remove valvebody and air check 1st clutch apply through case passage.
4. This step targets the specific mechanical failure.

Clutch Leaks:
^ Remove end cover and check for damaged 1st gear hub seal rings and check for blocked passage in cover or case.
^ If seal rings are ok remove 1st clutch and replace leaking piston.
^ Servo leak causing loss of 1st oil pressure. Remove valvebody and air check and check 1st oil pressure passage to servo. On 1993 and 1994 vehicles check 1, 3, 4 passage to servo.

No Blockage in Passages:
^ 1st gear sprag failed.
^ 1st clutch plates failed as a result of low line pressure or inadequate lube.
^ Output shaft broken.
^ Incorrect gear ratio installed.

DIAGNOSTIC AIDS
^ To air check 1st clutch use pressure apply points. Apply compressed air with rubber nozzle on air gun.

IMPORTANT: 1st gear is a mechanical hydraulic apply. Other than line pressure there is no electrical circuit that affects this gear.

^ DTC 16 - No 1st Gear may be set under certain conditions if an intermittent loss of vehicle speed signal occurs. If customer is also experiencing speedometer problems check the VSS circuit as a possible cause of DTC 16.