Circuit Description
The Transmission Control Module (TCM) calculates ratio based on the Automatic Transmission Input Speed (A/T ISS) Sensor and Output Shaft Speed (OSS) Sensor readings. The TCM compares the known transmission ratio to the calculated ratio, for the particular gear range selected.
DTC 86 will set when transmission commanded gear is 1st or 2nd and the transmission is mechanically in 3rd or 4th gear. DTC 86 is used to detect a 2-3 shift solenoid or hydraulic circuit malfunction.
Conditions for Setting the DTC
| • | No DTC(s) 21, 22, 24, 28, 71, 72 and 74. |
| • | Transmission is not in P, R, N. |
| • | Engine speed is greater than 300 RPM. |
| • | TP is greater than 25%. |
| • | Vehicle speed is greater than 11 km/h (7 mph). |
| • | Transmission gear ratio is less than 1.06 with commanded 1st or 2nd gear. |
| • | TFT is greater than 24.5°C (76°F). |
| • | All conditions are met for 2 seconds. |
Action Taken When the DTC Sets
| • | The TCM does not illuminate the Malfunction Indicator Lamp (MIL). |
| • | The TCM will command 2nd gear. |
| • | The TCM will command maximum line pressure. |
| • | The TCM will inhibit TCC engagement. |
| • | DTC 86 is stored in TCM history. |
Conditions for Clearing the DTC
| • | The TCM clears the DTC from Current to History when the fault condition(s) no longer exist and the ignition switch is cycled OFF and then ON. |
| • | A scan tool can clear the DTC from Current and History status. The TCM clears the DTC from the TCM history if the vehicle completes 40 ignition cycles without a failure reported. |
| • | The TCM cancels the DTC default actions when the fault no longer exists and the ignition is cycled OFF and then ON. |
The fault condition(s) no longer exist, and the ignition switch is cycled OFF long enough to power down the TCM, and then ON.
Diagnostic Aids
| • | First diagnose and clear any engine DTCs that are present. Then inspect for any transmission DTCs that may have reset. |
| • | Verify that the transmission meets the specifications in the Shift Speed table. |
| • | Other internal transmission failures may cause more than one shift to occur. |
| • | The customer may complain of an engine over-rev condition or neutral condition in 4th gear. |
| • | Refer to Shift Solenoid Valve State and Gear Ratio table. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the function of the TFP Val. Position Sw.
-
This step tests for a selected gear ratio versus a ratio not obtainable under normal driving conditions.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||
Important:: Before clearing the DTC's, record the Current and History DTC's information for reference. The Clear Info function erases the stored Current and History DTC from the TCM. Does each selected transmission range match the Scan Tool TFP Switch A/B/C display? (Refer to Range Signal ). | -- | Go to DTC 28 | ||||||
Drive the vehicle with the transmission in the D 4 range. Was 1st gear commanded and not achieved, or 4th gear commanded and another gear occurred? | -- | Go to Diagnostic Aids | ||||||
4 |
Did you find and correct the condition? | -- | -- | |||||
5 | In order to verify your repair, perform the following procedure:
Are the gear ratios within the specified range for each of the selected gears? | 1st: 2.38-2.63 2nd: 1.43-1.58 3rd: 0.95-1.05 4th: 0.73-0.77 | System OK | Begin Diagnosis again. |
