Circuit Description
As the wheel is rotated, the speed sensor produces an AC voltage that increases with wheel speed. The electronic brake control module (EBCM) uses the frequency of the AC signal to calculate the 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
DTC C1200 can be set anytime the key is ON and the EBCM has detected an open, short to ground, or a short to battery on the left front wheel speed circuit.
Action Taken When the DTC Sets
| • | The solenoid relay opens, removing power from the pump motor and solenoids. |
| • | DTC C1200 is stored. |
| • | ABS disabled, ABS warning lamp turns ON. |
Conditions for Clearing the DTC
| • | If the conditions that set the DTC C1200 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 of wiring for damage, shorts, and contamination |
| • | Inspection for improperly formed and/or damaged terminals |
| • | Checking terminal contact retention force by using a spare male/female terminal |
| • | Removal of the terminals from the connectors to check for proper terminal to wire crimp |
If the driver comments reflect that the ABS warning lamp is ON only during moist environmental changes, such as, rain, snow, vehicle wash, the 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 salt-water 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.
When measuring the wheel speed sensor resistance, ensure the vehicle is at room temperature, since resistance will increase with temperature.
Failure to perform the previous steps carefully and fully can result in misdiagnosis, unnecessary component replacement, and reccurrence of DTC C1200.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - ABS? | -- | Go to Step 2 | |
2 |
Is any physical damage noted? | -- | Go to Step 3 | Go to Step 4 |
3 | Repair the damage to the left front wheel speed sensor, jumper harness, and/or the toothed ring. Did you find and correct the condition? | -- | System OK | -- |
4 | Test-drive the vehicle at various speeds and over various road surfaces. Did DTC C1200 reset? | -- | Go to Step 6 | Go to Step 5 |
5 | DTC C1200 is intermittent. Refer to Diagnostic System Check - ABS . Did you find and correct the condition? | -- | System OK | -- |
6 |
Is the resistance within the specified range? | 800-1600 ohms | Go to Step 8 | Go to Step 7 |
7 | Replace the left front wheel speed sensor. Refer to Front Wheel Speed Sensor Replacement . Did you complete the replacement? | -- | System OK | -- |
8 |
Is the resistance within the specified value? | OL (open circuit) | Go to Step 9 | Go to Step 7 |
9 |
Is the resistance measured less than the specified value? | 2 ohms | Go to Step 11 | Go to Step 10 |
10 | Repair the source open or high resistance between terminals 20 and 2. Did you find and correct the condition? | -- | System OK | -- |
11 |
Is the resistance measured less than the specified value? | 2 ohms | Go to Step 4 | Go to Step 12 |
12 | Repair the open or high resistance between terminals 19 and 1. Did you find and correct the condition? | -- | System OK | -- |
13 |
Is the voltage less than the specified value? | 1 V | Go to Step 15 | Go to Step 14 |
14 | Repair the source open or high resistance between terminals 20 and 2. Did you find and correct the condition? | -- | System OK | -- |
15 |
Is the voltage less than the specified value? | 1 V | Go to Step 17 | Go to Step 16 |
16 | Repair the short to voltage between terminals 19 and 1. Did you find and correct the condition? | -- | System OK | -- |
17 |
Is the resistance measured equal to the specified value? | OL (open circuit) | Go to Step 19 | Go to Step 18 |
18 | Repair the short to ground between terminals 20 and 2. Did you find and correct the condition? | -- | System OK | -- |
19 |
Is the resistance measured equal to the specified value? | OL (open circuit) | Go to Step 21 | Go to Step 20 |
20 | Repair the short to ground between terminals 19 and 1. Did you find and correct the condition? | -- | System OK | -- |
21 |
Is the resistance measured equal to the specified value? | OL (open circuit) | Go to Step 23 | Go to Step 22 |
22 | Repair the short between the 2 circuits Did you find and correct the condition? | -- | System OK | -- |
23 |
Did the DTC C1200 reset? | -- | Go to Step 24 | System OK |
24 | Replace the EBCM. Refer to Brake Pressure Modulator Valve Assembly Replacement . Did you complete the replacement? | -- | System OK | -- |
