Auto A/C Diagnosis
DTC U0151: SRS-ECU Time-OutCAUTION:
- If DTC U0151 is set in the A/C-ECU, diagnose the CAN main bus line.
- Whenever the ECU is replaced, ensure that the communication circuit is normal.
TROUBLE JUDGMENT
The A/C-ECU receives air conditioning operation-related signals from the SRS-ECU via the CAN bus lines. If any of the air conditioning control-related signals from the SRS-ECU cannot be received, the diagnostic trouble code U0151 is stored.
TECHNICAL DESCRIPTION (COMMENT)
Current trouble
- Connector(s) or wiring harness in the CAN bus lines between the SRS-ECU and the A/C-ECU, the power supply system to the SRS-ECU, the SRS-ECU itself, or the A/C-ECU may be defective.
Past trouble
- If DTC U0151 is stored as a past trouble, carry out diagnosis with particular emphasis on wiring and connector(s) in the CAN bus line between the A/C-ECU and the SRS-ECU, and the power supply system to the SRS-ECU. If the connectors and wiring are normal, and obviously the ECU is the cause of the trouble, replace the ECU. If in doubt, do not replace the ECU.
NOTE: For a past trouble, you cannot find it by the scan tool CAN bus diagnostics even if there is a failure in CAN bus lines. Check the CAN bus lines. You can narrow down the possible cause of the trouble by referring to the DTC, which is set regarding the CAN communication-linked ECUs (Refer to Explanation about the scan tool CAN bus diagnostics). Can Bus Diagnostics Table
TROUBLESHOOTING HINTS
- Malfunction of the SRS-ECU
- Malfunction of the A/C-ECU
- Damaged harness wires and connectors
DIAGNOSIS
Required Special Tools:
- MB991223: Harness Set
- MB992006: Extra Fine Probe
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A
STEP 1. Using scan tool MB991958, diagnose the CAN bus line
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. Refer to "How to connect the Scan Tool (M.U.T.-III)." How to Connect the Scan Tool (M.U.T.-III)
2. Turn the ignition switch to the "ON" position.
3. Diagnose the CAN bus line.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the CAN bus line found to be normal?
YES : Go to Step 2.
NO : Repair the CAN bus line.
STEP 2. Using scan tool MB991958 read the SRS-ECU diagnostic trouble code.
Check whether an SRS-ECU DTCs are set or not
1. Turn the ignition switch to the "ON" position
2. Check for SRS-ECU DTCs.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?
YES : Diagnose the SRS-ECU (Refer to Diagnostic Trouble Code). Diagnostic Trouble Code Descriptions
NO : Go to Step 3.
STEP 3. Using scan tool MB991958, check for any diagnostic trouble code.
Check if a DTC, which relates to CAN communication-linked systems below, is set.
- ETACS-ECU
DTC indicating a time-out error related to the SRS-ECU system
1. Turn the ignition switch to the "ON" position.
2. Check for a DTC related to the relevant system
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?
YES : Go to Step 4.
NO : Go to Step 5.
STEP 4. Recheck for diagnostic trouble code.
Check again if the DTC is set.
1. Turn the ignition switch to the "ON" position
2. Check if the DTC is set.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?
YES : Replace the SRS-ECU. On completion, check that the DTC is not reset.
NO : There is an intermittent malfunction such as poor engaged connector(s) or open circuit.
STEP 5. Recheck for diagnostic trouble code.
Check again if the DTC is set.
1. Turn the ignition switch to the "ON" position
2. Check if the DTC is set.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?
YES : Replace the A/C-ECU. On completion, check that the DTC is not reset.
NO : There is an intermittent malfunction such as poor engaged connector(s) or open circuit.