Transmission Controls With PCM

Diagnostic Chart:

Wiring Diagram:

When a gear is commanded on, the vehicle speed to turbine speed ratio is monitored to assure the correct gear ratio. 4th gear stuck on indicates that another gear was commanded but the actual ratio driving the vehicle is equal to 4th gear. This is a calculated value (turbine speed/vehicle speed = gear ratio). 4th gear clutch is turned off by grounding Circuit 446 at the PCM.

INFORMATION FLAG PARAMETERS

Info. Flag 78 is set when the PCM has detected the following conditions twice per ignition cycle.

^ 1st gear selected by PCM.

^ Engine under load and load value is greater than 200.

^ No noise on turbine or vehicle speed signals.

^ Vehicle speed greater than 5 Km/h (3 mph).

^ Turbine speed greater than 224 rpm.

^ Speed ratio across torque converter less than 180, 255 = TCC on. Calculated from engine speed versus turbine speed.

^ Turbine speed to vehicle speed ratio equals 4th gear for more than five seconds.


TEST DESCRIPTION

Numbered steps below refer top numbered steps on chart.


1. Problem causing Info. Flags 76, 77 or 99 must be eliminated first as a possible cause of Info. flag 78.

2. Use actuator quick check. Actuator quick test will PWM actuator at a set rate. Listen an compare 4th gear actuator with another actuator; movement/noise should be similar.

3. Problem could be a mechanical failure. This step begins internal diagnosis.

4. Cross leaks to/from 3rd clutch oil passages can cause 3rd clutch to be on at all times.

5. As air pressure is applied and released, the clutch plates should also apply and release. If the clutch plates are moving normally, the problem is in the valve body. If clutches are not moving correctly, the problem is in the end cover or an internal transaxle problem exists.



DIAGNOSTIC AIDS

When attempting to diagnose an intermittent problem use the Scan tool* to review supplemental diagnostic information. The supplemental data can be used to duplicate a problem.

* Select MALF History from Scan tool TC menu.


Check the tightness of the female terminal grip with a spare male terminal.

When the PCM detects a fault in the circuit (open, ground, short) the PCM will open the circuit internally to protect the circuit.