Transmission Controls With PCM

Diagnostic Chart:

Wiring Diagram:

2ND GEAR STUCK ON
When a gear is commanded the vehicle speed to turbine speed ratio is monitored to assure the correct gear ratio. Second gear stuck on indicates that 1st gear was commanded but the actual ratio driving the vehicle is equal to 2nd gear. This is a calculated value TSS rpm/VSS rpm speed (Turbine Speed Sensor/Vehicle Speed Sensor = gear ratio). Second gear clutch is turned off by grounding circuit 581 at the PCM.

DTC PARAMETERS
DTC 21 is set when the PCM has seen the following conditions for more than three seconds twice per ignition cycle.
^ 1st gear commanded by PCM.
^ No noise detected on turbine or vehicle speed signals.
^ Vehicle speed greater than 5 km/h (3 mph).
^ Turbine speed greater than 224 rpm.
^ Speed ratio across the torque converter, engine speed versus turbine speed, less than 180. A speed ratio of 255 would be TCC on.
^ PCM calculated engine load value is greater than 200.
^ The ratio of turbine speed to vehicle speed equals that of 2nd gear.

TEST DESCRIPTION
1. Check for information flags 71, 72, or 97. They must be eliminated first as a possible cause of DTC 21.
2. Check actuator operation. Use actuator quick check. The actuator quick check will Pulse Width Modulate (PWM) the actuators at a set rate. Listen and compare noise of 2nd gear actuator to that of other actuators. The noise of all should be similar.
3. Perform 2nd clutch air check. Apply compressed air with rubber nozzle on air gun. Problem could be a mechanical failure. This step begins internal diagnosis.
4. Cross leaks to/from 2nd clutch circuit can cause 2nd clutch to be on at all times. If DTC 21 is present and there is no reverse, check end cover input hub seals.
5. As air pressure is applied and released, the clutch plates should also apply and release. If clutch plates are moving normally and no other leaks detected, the problem is probably in the valvebody. If clutches are not moving correctly, the problem is in the end cover or an internal clutch assembly problem.

DIAGNOSTIC AIDS
^ When the PCM detects a fault in the circuit (open, ground, short), the PCM will open the circuit internally to protect the circuit.
^ Could be a hot or cold only condition. If condition is intermittent, try to reproduce conditions in MALF table to reset the DTC.
^ Problem could be internal. Possible hydraulic leak, seals, gaskets, porosity, etc.
^ This DTC may set or intermittent 2nd gear starts may be caused by a poor electrical connection at either the PCM actuator connector plate or Underhood Junction Block (UHJB) terminals. Wiggling connectors while performing an actuator quick test may help isolate the problem area.