Inspection Procedure 17

INSPECTION PROCEDURE 17: Vehicle Speed Signal System









CIRCUIT OPERATION
^ While the vehicle is being driven, the PCM sends pulse signals (ranging from 0 to 12 volts) to the combination meter according to output signals from the output shaft speed sensor. The combination meter displays vehicle speed according to the pulse signals.
^ If the vehicle speed signal becomes inoperative, the transaxle will not shift normally.

COMMENTS
Failure may occur on vehicle speed signal circuit, speedometer and PCM.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set:)
^ Malfunction of the output shaft speed sensor
^ Malfunction of the speedometer
^ Damaged harness, connector
^ Malfunction of the PCM

DIAGNOSIS
Required Special Tool: MB991502: Scan Tool (MUT-II)

STEP 1. Check the speedometer.
Q: Is the speedometer operating properly?
YES: Go to Step 2.
NO: Check the speedometer.





STEP 2. Using scan tool MB991502, read the A/T diagnostic trouble code.

CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.

1. Connect scan tool MB991502 to the data link connector.
2. Turn the ignition switch to "ON" position.
3. Read the A/T diagnostic trouble code.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is A/T diagnostic trouble code number "23" output?
YES: Refer to Output Shaft Speed Sensor System.
NO: Go to Step 3.





STEP 3. Using scan tool MB991502, check data list item 29: Vehicle Speed Signal.

CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.

1. Connect scan tool MB991502 to the data link connector.
2. Start the engine.
3. Set scan tool MB991502 to data reading mode for item 29: Vehicle Speed Signal.
^ Check that the speedometer and scan tool display speed match when driving at a vehicle speed of 40 km/h (25 mph).
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: This malfunction is intermittent.
NO: Go to Step 4.

STEP 4. Using the oscilloscope, check the waveform at PCM connector C-41.





1. Do not disconnect connector C-41.





2. Connect an oscilloscope probe to PCM connector C-41 terminal 80 by backprobing.
3. Raise the vehicle a hoist and prepare to run the vehicle. Start the engine.





4. Check the waveform.
^ The waveform should show a pattern similar to the illustration when running the vehicle.
5. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the waveform normal?
YES: Go to Step 5.
NO: Go to Step6.

STEP 5. Check connector C-41 at PCM for damage.





Q: Is the connector in good condition?
YES: Go to Step 8.
NO: Repair or replace it.








STEP 6. Check connectors C-41 at PCM, C-17 at intermediate connector, C-56 Joint connector and C-30 Combination meter connector for damage.
Q: Are the connectors in good condition?
YES: Go to Step 7.
NO: Repair or replace the defective connector(s).








STEP 7. Check harness for open circuit or damage between PCM connector C-41 terminal 80 and combination meter connector C-30 terminal 16.
Q: Is the harness wire in good condition?
YES: Go to Step 8.
NO: Repair it.





STEP 8. Using scan tool MB991502, check data list item 29: Vehicle Speed Signal.

CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.

1. Connect scan tool MB991502 to the data link connector.
2. Start the engine.
3. Set scan tool MB991502 to data reading mode for item 29, Vehicle Speed Signal.
^ Check that the speedometer and scan tool display speed match when driving at a vehicle speed of 40 km/h (25 mph).
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: This malfunction is intermittent.
NO: Replace the PCM.