GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Chevy P32 RV/Van Chassis 🢒 DTC 🢒 DTC 87 High Ratio Error

DTC 87 High Ratio Error L57 MFI


Object Number: 230247 Size: MF
Automatic Transmission Components Diesel
Automatic Transmission Controls Schematics TCM Control

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 87 sets when transmission commanded gear is 3rd or 4th and the transmission is mechanically in 1st or 2nd gear. DTC 87 is used to detect a 2-3 shift solenoid or hydraulic circuit malfunction.

Conditions for Running the DTC
    • No DTCs 21, 22, 24, 28, 71, 72 and 74.
    • Transmission fluid temperature is greater than 24.5°C (76°F).
    • TP angle is greater than 25%.
    • Not in P, R, N.
    • Engine speed greater than 300 RPM.
    • Vehicle speed is greater than 11 km/h (7 mph).

Conditions for Setting the DTC
    • Transmission gear ratio is greater than 1.42 with commanded 3rd or 4th gear.
    • All conditions are met for 5 seconds.

Action Taken When the DTC Sets
    • The TCM does not illuminate the malfunction indicator lamp (MIL).
    • The TCM commands 2nd gear.
    • The TCM commands maximum line pressure.
    • The TCM inhibits TCC engagement.
    • The TCM stores DTC 87 in TCM history.

Conditions for Clearing the DTC
    • A scan tool clears the DTC from TCM history.
    • The TCM clears the DTC from TCM history if the vehicle completes 40 consecutive key cycles without a diagnostic fault occurring.
    • The TCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the TCM.

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.

  1. This step tests the function of the TFP manual valve position switch.

    2.

  2. This step tests for a selected gear ratio versus a ratio not obtainable under normal driving conditions.

DTC 87

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install the Scan Tool .
  2. With the engine OFF, turn the ignition switch to the RUN position.

    3. Important:: Before clearing the DTCs, use the scan tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the TCM.

  3. Record the Failure Records.
  4. Clear the DTC.
  5. Select TFP Sw. A/B/C on the Scan Tool .
  6. With the engine running, apply the brake pedal and select each transmission range: D1, D2, D3, D4, N, R and P.

Refer to the Range Signal table.

Does each selected transmission range match the TFP Switch A/B/C display?

--

Go to Step 3

Go to DTC 28 TFP Manual Valve Position Switch Fault

3

Drive the vehicle with the transmission in the D4 range.

  1. Use the Scan Tool in order to command 1st, 2nd, 3rd and 4th gears while accelerating the vehicle.
  2. Note the gear ratio in THIRD gear and FOURTH gear.

Was the ratio for commanded THIRD or FOURTH gear greater than 1.42?

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Inspect the 2-3 shift solenoid valve or the 2-3 hydraulic shift valve for an internal malfunction.
  2. Inspect the shift solenoid/hydraulic for damaged seals.

    3. Refer to Symptom Diagnosis .

Was the condition corrected?

--

Go to Step 5

--

5

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle under the following conditions (only if traffic conditions permit):
    4. • The TCM must see the proper gear ratio for each gear, for greater than one second in D1, D2, D3 and D4.
    • Hold the throttle at greater than 12% to obtain 4th gear.

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

Go to Step 1