DTC 21
DTC 21: ABS Sensor
CIRCUIT OPERATION
^ A toothed ABS rotor generates a voltage pulse as it moves across the pickup field of each ABS sensor.
^ The amount of voltage generated at each wheel is determined by the clearance between the ABS rotor teeth and the ABS sensor, and by the speed of rotation.
^ The ABS sensors transmit the frequency of the voltage pulses and the amount of voltage generated by each pulse to the ABS electronic control unit (ABS-ECU).
^ The ABS hydraulic unit modulates the amount of braking force individually applied to each wheel cylinder.
ABS DTC SET CONDITIONS
DTCs 21, 22, 23, 24 are output in the following cases:
^ Open circuit is not found but no input is received by one or more of the four ABS sensors at 10 km/h (6 mph) or more.
^ ABS sensor output drops due to a malfunctioning ABS sensor or warped ABS rotor.
TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THESE DTCS ARE TO SET ARE:)
^ Malfunction of the ABS sensor
^ Damaged wiring harness or connector
^ Malfunction of the hydraulic unit (integrated with ABS-ECU)
^ Malfunction of the ABS rotor
^ Malfunction of the wheel bearing
^ Excessive clearance between the ABS sensor and ABS rotor
DIAGNOSIS
Required Special Tools:
^ MB991223: Harness Set
^ MB991958: Scan Tool (MUT-III Sub Assembly)
^ MB991824: Vehicle Communication Interface
^ MB991827: MUT-III USB Cable
^ MB991910: MUT-III Main Harness A
^ MB991529: Diagnostic Trouble Code Check Harness
STEP 1. Using scan tool MB991958, check data list.
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 the data reading mode, and check the data list items by driving the vehicle.
^ Item 01 (DTC 11 is set): Front right ABS sensor
^ Item 02 (DTC 12 is set): Front left ABS sensor
^ Item 03 (DTC 13 is set): Rear right ABS sensor
^ Item 04 (DTC 14 is set): Rear left ABS sensor
4. Turn the ignition switch to the LOCK (OFF) position.
Q: Is the ABS sensor input normal?
YES: This malfunction is intermittent.
NO: Go to Step 2.
STEP 2. Check the ABS sensor installation.
Q: Is the ABS sensor bolted securely in place at the front knuckle or the rear knuckle?
YES: Go to Step 3.
NO: Install it properly. and go to Step 11
STEP 3. Inspect the ABS sensor and ABS rotor.
Check items:
^ ABS sensor internal resistance: 1.24 - 1.64 k Ohms
^ Insulation between the ABS sensor body and the connector terminals
^ Toothed ABS rotor check
Q: Is the ABS sensor or ABS rotor damaged?
YES: Replace it and then go to Step 11.
NO: Go to Step 4.
STEP 4. Check ABS sensor circuit at the ABS-ECU connector B-03.
1. Disconnect the connector B-03 and measure at the harness side.
2. Measure the resistance between the ABS-ECU connector terminals 16 and 26, 9 and 10, 11 and 17, or 27 and 28.
Standard Value: 1.24 - 1.64 k Ohms
Q: Is the resistance between terminals 16 and 26,9 and 10, 27 and 28, or 11 and 17 within the standard value?
When resistances between all terminals are within the standard value.: Go to Step 9.
When resistance between terminals 16 and 26 is not within the standard value.: Go to Step 5.
When resistance between terminals 9 and 10 is not within the standard value.: Go to Step 6.
When resistance between terminals 27 and 28 is not within the standard value.: Go to Step 7.
When resistance between terminals 11 and 17 is not within the standard value.: Go to Step 8.
STEP 5. Check the harness wires between ABS-ECU connector B-03 terminal 16 and ABS sensor
NOTE: After inspecting ABS-ECU connector B-03, intermediate connector A-14 and ABS sensor
Q: Is the harness wire between ABS-ECU connector B-03 terminal 16 and ABS sensor
YES: Repair it and go to Step 11.
NO: Go to Step 11.
STEP 6. Check the harness wires between ABS-ECU connector B-03 terminal 10 and ABS sensor
NOTE: After inspecting ABS-ECU connector B-03, intermediate connector C-14, C-104 and ABS sensor
Q: Is the harness wire between ABS-ECU connector B-03 terminal 10 and ABS sensor
YES: Repair it and go to Step 11.
NO: Go to Step 11.
STEP 7. Check the harness wires between ABS-ECU connector B-03 terminal 28 and ABS sensor
NOTE: After inspecting ABS-ECU connector B-03, intermediate connector C-104, C-117, D-22 and ABS sensor
Q: Is the harness wire between ABS-ECU connector B-03 terminal 28 and ABS sensor
YES: Repair it and then go to Step 11.
NO: Go to Step 11.
STEP 8. Check the harness wires between ABS-ECU connector B-03 terminal 11 and ABS sensor
NOTE: After inspecting ABS-ECU connector B-03, intermediate connector C-104, C-117, D-22 and ABS sensor
Q: Is the harness wire between ABS-ECU connector B-03 terminal 11 and ABS sensor
YES: Repair it and then go to Step 11.
NO: Go to Step 11.
STEP 9. Check the ABS sensor output voltage.
Output Voltage:
^ When measured with a voltmeter: 42 mV or more
^ When measured with an oscilloscope (maximum voltage): 200 mV or more
Q: Does the voltage meet the specification?
YES: Erase the DTC memory, and recheck if any DTC sets. If DTC 21, 22, 23 or 24 sets, replace the hydraulic unit (integrated with ABS-ECU). Then go to Step 11.
NO: Go to Step 10.
STEP 10. Check the wheel bearing.
If play on the wheel bearing is not within the standard value, replace the wheel bearing.
Limit Value: 0.05 mm (0.002 inch)
Q: Is play on the wheel bearing within the standard value?
YES: Go to Step 11.
NO: Replace it and then go to Step 11.
STEP 11. Recheck for diagnostic trouble codes.
Q: Do the diagnostic trouble codes 21, 22, 23 or 24 reset?
YES: Go to Step 1.
NO: The procedure is complete.