Circuit Description
As the wheel is rotated, the speed sensor produces an alternating current (AC) voltage that increases with wheel speed. The electronic brake control module (EBCM) uses the frequency of the AC signal to calculate wheel speed. The speed sensor is connected to the EBCM by a twisted pair of wires. Twisting reduces noise susceptibility that may cause a DTC to set.
Conditions for Setting the DTC
All of the following must be true for DTC C0027 to set:
| • | DTCs C0032, C0033, C0034, or C0035 are not current. |
| • | The brake switch is OFF. |
| • | The left rear wheel speed is accelerating or decelerating beyond reasonable limits. |
Action Taken When the DTC Sets
| • | The solenoid relay opens, removing power from the pump motor and solenoids. |
| • | DTC C0027 is stored. |
| • | The antilock brake system (ABS) is disabled, ABS warning lamp turns ON. |
Conditions for Clearing the DTC
| • | If the conditions that set DTC C0027 are no longer present, the DTC may be cleared by using the proper scan tool. |
| • | The DTC that has not occurred in 100 drive cycles will be cleared from history data. |
Diagnostic Aids
Thoroughly inspect the wiring and connectors when diagnosing intermittent DTCs. This will include the following:
| • | Removal of the protective conduit and inspection for wiring for damage, shorts, and contamination |
| • | Inspection for improperly formed and/or damaged terminals |
| • | Inspecting terminal contact, retention force, by using a spare male/female terminal |
| • | Removal of the terminals from the connectors to inspect for proper terminal to wire crimp |
If the drivers comments reflect that the ABS warning lamp is ON only during moist environmental changes, such as rain, snow, vehicle wash, etc., all wheel speed sensor circuitry should be thoroughly inspected for signs of water intrusion. If the DTC is not current, simulate the effects of water intrusion. Use the following procedure. Spray the suspected area with a 5 percent saltwater solution. Then test drive the vehicle over various road surfaces such as bumps, turns, etc., above 24 km/h (15 mph). If the DTC sets then replace the suspected harness and/or sensor.
A careful visual inspection of the toothed ring for damage such as cracks and tooth damage should be performed. If the DTC sets at the same speed every drive cycle, the toothed ring is most likely damaged.
Failure to perform the previous steps carefully and fully can result in misdiagnosis, unnecessary component replacement, and reoccurrence of DTC C0027.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-ABS? | -- | Go to Step 2 | |
2 | Was DTC C0034 set as a current or history DTC? | -- | Go to DTC C0034 | Go to Step 3 |
3 |
Is any physical damage noted? | -- | Go to Step 4 | Go to Step 5 |
4 | Repair the damage to the left rear wheel speed sensor, jumper harness, and/or the toothed ring. Did you complete the repair? | -- | System OK | -- |
5 |
Did DTC C0027 reset or did the left rear wheel speed read above 0 mph when the vehicle was in park with the engine running? | -- | Go to Step 6 | Go to Step 7 |
6 | The cause of DTC C0027 is ignition noise coupled onto the left rear speed sensor circuits.
Did you find and correct the condition? | -- | System OK | -- |
7 |
Did DTC C0027 reset or did the left rear wheel speed vary more than 5 km/h (3 mph) when compared to any one of the other wheels during the drive? | -- | Go to Step 9 | Go to Step 8 |
8 | DTC C0027 is intermittent. Refer to Diagnostic Aids. Did you find and correct the condition? | -- | System OK | -- |
9 |
Important: Resistance will vary with temperature. Is the resistance within the specified range? | 800-1600 ohms | Go to Step 11 | Go to Step 10 |
10 | Replace the left rear wheel speed sensor. Did you complete the replacement? | -- | System OK | -- |
11 |
Does the AC voltage measure greater than the specified value? | 100 mV | Go to Step 12 | Go to Step 10 |
12 |
Does the resistance measure less than the specified value? | 2 ohms | Go to Step 14 | Go to Step 13 |
13 | Repair the source open or high resistance between terminals A10 and 1. Did you complete the repair? | -- | System OK | -- |
14 |
Does the resistance measure less than the specified value? | 2 ohms | Go to Step 16 | Go to Step 15 |
15 | Repair the open or high resistance between terminals A9 and 2. Did you complete the repair? | -- | System OK | -- |
16 |
Does the resistance measure OL, open circuit? | OL (Open Circuit) | Go to Step 18 | Go to Step 17 |
17 | Repair the short between the 2 wires. Did you complete the repair? | -- | System OK | -- |
18 |
Did DTC C0027 reset? | -- | Go to Step 19 | System OK |
19 | Replace the EBCM. Did you complete the replacement? | -- | System OK | -- |
