Inspection Procedure 17

INSPECTION PROCEDURE 17: Vehicle Speed Signal System

Part 1 Of 2:

Part 2 Of 2:

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.

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

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

DIAGNOSIS

Required Special Tool:
^ MB991958: Scan Tool (MUT-III Sub Assembly)
^ MB991824: V.C.I.
^ MB991827: MUT-III USB Cable
^ MB991911: MUT-III Main Harness B

STEP 1. Using scan tool MB991958, read the A/T diagnostic trouble code.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.





1) Connect scan tool MB991958 to the data link connector.
2) Turn the ignition switch to the "ON" position.
3) Check for A/T diagnostic trouble code.
4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is DTC 23 set?
YES: Refer to DTC 23: Output Shaft Speed Sensor System.
NO: Go to Step2.

STEP 2. Using scan tool MB991958, check data list item 29: Vehicle Speed Signal.





1) Connect scan tool MB991958 to the data link connector.
2) Start the engine.
3) Set scan tool MB991958 to data reading mode for item 29: Vehicle Speed Signal.
^ Check that the speedometer and scan tool MB991958 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: It can be assumed that this malfunction is intermittent.
NO: Go to Step 3.

STEP 3. Using an oscilloscope, check the vehicle speed signal waveform at PCM connector C-57 <2.4L Engine> or C-59 <3.0L Engine> by backprobing.





1) Do not disconnect connector C-57 <2.4L Engine> or C-59 <3.0L Engine>.





2) Connect an oscilloscope probe to PCM connector C-57 <2.4L Engine> or C-59 <3.0L Engine> terminal 80 by backprobing.
3) Start the engine and drive the vehicle.





4) Check the vehicle speed signal waveform.
^ The vehicle speed signal waveform should show a pattern similar to the illustration. The maximum value should be 11 volts and more and the minimum value 0.6 volt and less. The output waveform should not contain electrical noise
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 PCM connector C-57 <2.4L Engine> or C-59 <3.0L Engine> for loose, corroded or damaged terminals, or terminals pushed back in the connector.





Q: Are the connector and terminals in good condition?
YES: Go to Step 8.
NO: Repair or replace the damaged components.

STEP 5. Check PCM connector C-57 <2.4L Engine> or C-59 <3.0L Engine>, intermediate connector C-28, joint connector C-77 and combination meter connector C-42 for loose, corroded or damaged terminals, or terminals pushed back in the connector.














Q: Are the connectors and terminals in good condition?
YES: Go to Step 6.
NO: Repair or replace the damaged components.

STEP 6. Check the harness for open circuit, short circuit to ground or damage between PCM connector C-57 <2.4L Engine> or C-59 <3.0L Engine> terminal 80 and combination meter connector C-42 terminal 30.








Q: Is the harness wire in good condition?
YES: Go to Step 7.
NO: Repair or replace the harness wire.

STEP 7. Check the speedometer.
Q: Is the speedometer operating properly?
YES: Go to Step 8.
NO: Replace the combination meter.

STEP 8. Using scan tool MB991958, check data list item 29: Vehicle Speed Signal.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.





1) Connect scan tool MB991958 to the data link connector.
2) Start the engine.
3) Set scan tool MB991958 to data reading mode for item 29: Vehicle Speed Signal.
^ Check that the speedometer and scan tool MB991958 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.