Inspection Procedure 4: In Spite of Abnormally Low Tire Pressure at A Road Wheel, the TPMS Warning Light Does Not Illuminate

INSPECTION PROCEDURE 4: In Spite of Abnormally Low Tire Pressure at a Road Wheel, the TPMS Warning Light does not Illuminate.

SYSTEM OPERATION
The TPMS warning light will illuminate when the ignition switch is turned to the "ON" position if tire pressure of any road wheel is low.

TECHNICAL DESCRIPTION (COMMENT)
- The TPMS may not detect a failure if the TPMS transmitter does not send timely information or there is any interference with the antenna.
- The tire pressure sensor or roll switch inside the TPMS transmitter may be inaccurate or defective. In this case, the TPMS may not detect a failure.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CASE:)
- The TPMS transmitter does not send timely information or there is any interference with the antenna.
- Damaged harness wire or connector
- Malfunction of the combination meter
- Malfunction of the TPMS transmitter
- Malfunction of the TPMS receiver

DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A

STEP 1. Check the TPMS warning light. TPMS Warning Light Check
Check whether the TPMS warning light illuminates for three seconds after the ignition switch is turned to the "ON" position.
Q:Does the TPMS warning light illuminate for three seconds?
YES: Check that the TPMS warning light illuminates for three seconds and then go out. Then go to Step 2.
NO: Go to TPMS Inspection Procedure No.3 "The TPMS Warning Light does not Illuminate as a Bulb Check for Three Seconds when the Ignition Switch is Turned to the "ON" Position".

STEP 2. Using scan tool MB991958, read the 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 whether DTC C1912, C1922, C1932 or C1942 (TPMS transmitter abnormality -Tire air pressure low) is set.

NOTE: If DTC C1912, C1922, C1932 or C1942 is set, the TPMS receiver is defective. In Step 1, the TPMS warning light illuminated for three seconds and then went out. However, the DTC is set. This means that a contradiction has arisen in the receiver operation.

Q:Is DTC C1912, C1922, C1932 or C1942 (TPMS transmitter abnormality -Tire air pressure low) set?
YES: Replace the TPMS receiver. Then go to Step 10.
NO: Go to Step 3.

STEP 3. Execute "Tire Pressure Sensor ID Check" and "Tire Pressure Sensor Check" on scan tool MB991958 "Special Function." Tire Pressure Sensor ID Check Tire Pressure Sensor Check
(1) Execute "Tire Pressure Sensor ID Check" on scan tool MB991958 "Special Function", and make a note of all the registered tire pressure sensor IDs. Tire Pressure Sensor ID Registration

NOTE: This note is needed when you check the registered IDs.

(2) Execute "Tire Pressure Sensor Check" on scan tool MB991958 "Special Function" for the relevant tire. Tire Pressure Sensor Check
(3) Confirm the tire inflation pressure and tire pressure sensor ID, which are shown on scan tool MB991958 display.
Q:Are the tire inflation pressure and tire pressure sensor ID displayed?
YES: Go to Step 4.
NO: It is judged that the TPMS could not detect abnormal reception due to a defective TPMS transmitter. Replace the relevant TPMS transmitter. Then go to Step 10.

STEP 4. Check the tire pressure sensor ID, which is shown on scan tool MB991958 display.
Compare the tire pressure sensor ID shown on scan tool MB991958 with the tire pressure sensor ID noted at Step 3.
Q:Is the tire pressure sensor ID shown on scan tool MB991958 the same as the noted ID?
YES: Go to Step 5.
NO: Go to Step 10.

STEP 5. Check the tire pressure, which is shown on scan tool MB991958 display.
Q:Is the shown tire inflation pressure less than the threshold value (174 kPa, 25.3 psi)?
YES: Go to Step 7.
NO: Go to Step 6.

STEP 6. Use an accurate tire pressure gauge to measure the relevant tire inflation pressure.
Compare the actually measured value with the value shown on scan tool MB991958 to determine whether the TPMS transmitter pressure sensor is inaccurate.

NOTE: In areas where atmospheric pressure is low (such as high altitude), scan tool MB991958 value will reduce accordingly. This is not a failure. For your reference, the value reduces approximately 3.5 kPa (0.5 psi) for every 305 m (1,000 feet).

Q:Is the tire inflation pressure shown on scan tool MB991958 within ± 10 kPa (1.5 psi) from the actual inflation pressure? [Ambient temperature during measurement must be 0-50° C (32-122°F)]
YES: The procedure is complete.
NO: Replace the TPMS transmitter of the relevant tire. Then go to Step 10.

STEP 7. Check the illumination condition of the TPMS warning light. TPMS Warning Light Check
Turn the ignition switch to the "ON" position. Check that the TPMS warning light illuminates for three seconds, goes out momentarily, and then illuminates again.
Q:Does the TPMS warning light illuminate again?
YES: Go to Step 8.
NO: Go to Step 9.

STEP 8. Check the relevant tire for improper inflation pressure or any other problems, and make necessary repairs. Then drive the vehicle and check if the TPMS warning light comes on. TPMS Warning Light Check
(1) If the relevant tire has been punctured, repair it. If the valve grommet or valve core is defective, replace it.
(2) Adjust the relevant tire inflation pressure to the value specified on the tire pressure label.
(3) Drive the vehicle, and check that the TPMS warning light goes out within 10 minutes after the vehicle speed reaches 30 km/h (19 mph).
Q:Does the TPMS warning light go out?
YES: The procedure is complete. (For some reason, the TPMS transmitter could not communicate with the TPMS receiver momentarily).
NO: The roll switch of the TPMS transmitter may be defective. Replace the TPMS transmitter of the relevant tire. Then go to Step 10.

STEP 9. Using scan tool MB991958, read the diagnostic trouble code.
Check whether DTC C1912, C1922, C1932 or C1942 (TPMS transmitter abnormality -Tire air pressure low) is set.
Q:Is DTC C1912, C1922, C1932 or C1942 (TPMS transmitter abnormality -Tire air pressure low) set?
YES: Replace the TPMS receiver. Then go to Step 10.
NO: Replace the TPMS receiver. Then go to Step 10.

STEP 10. Tire pressure sensor ID registration and TPMS check
(1) Execute "Tire Pressure Sensor ID Registration" on scan tool MB991958 "Special Function" when the relevant tire inflation pressure is lower than 154 kPa (22.3 psi).
(2) Check whether the TPMS warning light illuminates and DTC C1912, C1922, C1932 or C1942 (TPMS transmitter abnormality -Tire air pressure low) is set.
(3) If the relevant tire has been punctured, repair it. If the valve grommet or valve core is defective, replace it.
(4) Wait until the tires cool down, and adjust the relevant tire inflation pressure to the value specified on the tire pressure label.
(5) Use a magnet to force the TPMS transmitter to send a signal. The signal sending procedure is the same as executing "Tire Pressure Sensor Check" on scan tool MB991958 "Special Function". TPMS Special Function Data List
NOTE: By forcing the TPMS transmitter to send a signal, the transmitter informs the TPMS receiver of the correct tire inflation pressure. Then the warning light should go off.
(6) Check that the TPMS warning light is off.

Q:Does the TPMS warning light remain off?
YES: The procedure is complete.
NO: Repeat this Step.