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. 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 the "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" set?
YES: Refer to code number 23: Output Shaft Speed Sensor System.
NO: Go to Step 2.
STEP 2. Using scan tool MB991502, check dam 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 MUT-II 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 3.
STEP 3. Using an oscilloscope, check the waveform at PCM connector C-116.
1. Do not disconnect connector C-116.
2. Connect an oscilloscope probe to PCM connector C-116 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 4.
NO: Go to Step 5.
STEP 4. Check connector C-116 at PCM for damage.
Q: Is the connector in good condition?
YES: Go to Step 8.
NO: Repair or replace it.
STEP 5. Check connectors C-116 at PCM, C-124 at intermediate connector, C-21 Joint connector and C-1 Combination meter connector for damage.
Q: Are the connectors in good condition?
YES: Go to Step 6.
NO: Repair or replace the connectors.
STEP 6. Check harness for open circuit or damage between PCM connector C-116 terminal 80 and combination meter connector C-01 terminal 12.
Q: Is the harness wire in good condition?
YES: Go to Step 7.
NO: Repair it.
STEP 7. Check the speedometer.
Q: Is the speedometer operating properly?
YES: Go to Step 8.
NO: Repair it because of harness damage or short circuit to ground between joint connector C-140 terminal 20 and data link connector C-26 terminal 14.
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 MUT-II 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.