DTC 26

Part 1:

Part 2:

DTC 26: Stoplight Switch System

CIRCUIT OPERATION
^ Battery positive voltage is supplied to the stoplight switch (terminal 2).
^ When the brake pedal is depressed, battery positive voltage is applied to the PCM (terminal 123).

DTC SET CONDITIONS
If the stoplight switch is on for five minutes or more while driving above 50 km/h (31 mph), or all of the stop light bulbs are blown, it is judged there is a short circuit or open circuit in the stoplight switch. This causes DTC 26 to be set.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
^ Malfunction of the stoplight switch
^ Malfunction of stoplight bulb
^ Damaged harness or 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. Check the brake pedal height.
Q: Is the height adjusted properly?
YES: Go to Step 2.
NO: Adjust the brake pedal to the proper height.

STEP 2. Check the stoplight bulb.
Q: Is the stoplight bulb in good condition?
YES: Go to Step 3.
NO: Replace the stoplight switch.

STEP 3. Using scan tool MB991958, check data list item 26: Stoplight Switch.

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) Set scan tool MB991958 to the data reading mode.
^ Item 26: Stoplight Switch.
- When the brake pedal is depressed, the display on scan tool MB991958 should be "ON."
- When the brake pedal is not depressed, the display on scan tool MB991958 should be "OFF."

4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the switch operating properly?
YES: It can be assumed that this malfunction may be intermittent.
NO: Go to Step 4.

STEP 4. Measure the stoplight switch power supply voltage at connector C-102 by backprobing.

1) Remove the stoplight switch from the mounting bracket.
2) Do not disconnect connector C-102.

3) Measure the voltage between terminal 2 and ground by backprobing.
^ The voltage should measure battery positive voltage.
Q: Is the measured voltage battery positive voltage?
YES: Go to Step 7.
NO: Go to step 5.

STEP 5. Check stoplight switch connector C-102 and intermediate connector C-129 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 6.
NO: Repair or replace the damaged components.

STEP 6. Check the harness for damage between stoplight switch connector C-102 terminal 2 and the power supply fuse.

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

STEP 7. Measure the stoplight switch output voltage to the PCM at connector C-102 by backprobing.

1) Remove the stoplight switch from the mounting bracket.
2) Do not disconnect connector C-102.

3) Measure the voltage between terminal 1 and ground by backprobing.
^ When the switch button is out (closed circuit), voltage should equal battery positive voltage.
^ When the switch button is depressed (open circuit), voltage should measure less than 1.0 volt.
Q: Is the measured voltage battery positive voltage with the switch button released (closed circuit), and less than 1.0 volt with the switch button depressed (open circuit)?
YES: Go to Step 9.
NO: Go to Step 8.

STEP 8. Check the stoplight switch.

Q: Does the stoplight switch pass the checks?
YES: Go to Step 9.
NO: Replace the stoplight switch.

STEP 9. Measure the stoplight switch output voltage at the PCM connector C-114 by backprobing.
1) Install the stoplight switch into the mounting bracket if it was removed.

2) Do not disconnect connector C-114.

3) Measure the voltage between terminal 123 and ground.
^ When the brake pedal is depressed, voltage should be measured battery positive voltage.
^ When the brake pedal is not depressed, voltage should be measured less than 1.0 volt.
Q: Is the measured voltage battery positive voltage with the brake pedal depressed (closed circuit), and less than 1.0 volt with the brake pedal released (open circuit)?
YES: Go to Step 12.
NO: Go to Step 10.

STEP 10. Check joint connector (6) C-105, PCM connector C-114 and intermediate connector C-124 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 11.
NO: Repair or replace the damaged components.

STEP 11. Check the harness for damage between stoplight switch connector C-102 terminal 1 and PCM connector C-114 terminal 123.

Q: Is the harness wire in good condition?
YES: Go to Step 12.
NO: Repair or replace the harness wire.

STEP 12. Using scan tool MB991958, check data list item 26: Stoplight Switch.

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.