Circuit Description
DTC C1251 detects a stripped nut or gear assembly during initialization. During the homing sequence the piston should reach the top of the bore. Then the ABS motor stalls. If the ABS motor does not stall the ABS motor must be spinning with little or no resistance. This indicates a nut/screw or gear malfunction.
Conditions for Setting the DTC
DTC C1251 can only set during initialization. A malfunction exists if the feedback current is less than the command current for a specified period of time.
Action Taken When the DTC Sets
| • | A malfunction DTC stores. |
| • | The ABS/TCS disables. |
| • | The amber ABS/TCS warning indicators turn on. |
| • | The red BRAKE warning indicator turns on. |
Conditions for Clearing the DTC
| • | The condition responsible for setting the DTC no longer exists and the Scan Tool Clear DTC function is used. |
| • | 100 drive cycles pass with no DTC detected. |
Diagnostic Aids
The following conditions may cause an intermittent malfunction if the conditions exist in a mechanical part of the system:
| • | Sticking |
| • | Binding |
| • | Slipping |
Use the enhanced diagnostic function of the Scan Tool in order to measure the frequency of the malfunction. Refer to the Scan Tool manual or Scan Tool Diagnostics located in this section for the procedure. DTC C1251 may set after modulator disassembly if the modulator pistons are positioned at the bottom of the modulator piston bore. If DTC C1251 only occurs once and DTC C1264 also occurs, refer to DTC C1264 Rear ABS Motor Circuit Open . If intermittent and enhanced diagnostics shows this DTC occurs during ABS, refer to DTC C1264 Rear ABS Motor Circuit Open .
Depending on the frequency of the malfunction, a physical inspection of the mechanical parts suspected of causing the malfunction may be necessary.
Clear the DTCs after completing the diagnosis. Test drive the vehicle for three drive cycles in order to verify that the DTC does not reset. Use the following procedure in order to complete one drive cycle:
- Start the vehicle.
- Drive the vehicle over 16 km/h (10 mph).
- Stop the vehicle.
- Turn the ignition to the OFF position.
Important: Zero the J 39200 test leads before making any resistance measurements.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Diagnostic System Check performed? | -- | Go to Step 2 | |||||||||
2 |
Does DTC C1261 also set as a current DTC? | -- | Go to Step 3 | |||||||||
3 |
Are the rear ABS motor command current and the rear ABS motor feedback current within the specified current? | 9-11A | Go to Step 4 | Go to Step 6 | ||||||||
4 |
Have the following conditions been met?
| 5-7A | Go to Step 5 | Go to Step 6 | ||||||||
5 |
Does the brake pedal rise? | -- | Go to Step 22 | Go to Step 6 | ||||||||
6 |
Is the resistance less than or equal to the specified value? | 1.5ohms | Go to Step 7 | Go to Step 15 | ||||||||
7 | Use the J 39200 in order to measure the resistance between the 6-way ABS brake motor pack connector terminal C and the 8-way EBCM/EBTCM harness connector C2 terminal E. Is the resistance less than or equal to the specified value? | 1.5ohms | Go to Step 8 | Go to Step 16 | ||||||||
8 | Use the J 39200 in order to measure the resistance between the 6-way ABS brake motor pack connector terminal C and the 6-way ABS brake motor pack connector terminal D. Is the resistance less than or equal to the specified value? | 1.5ohms | Go to Step 9 | Go to Step 17 | ||||||||
9 |
(The ABS brake motor pack is the unit with the three small gears. The ABS brake motor pack rear gear is the middle gear when the ABS brake modulator is mounted in the vehicle.) Is the ABS brake motor rear gear stripped? | -- | Go to Step 17 | Go to Step 10 | ||||||||
10 | Inspect for a stripped ABS brake modulator rear gear. (The ABS brake modulator unit is the unit with the three large gears. The ABS brake modulator rear gear is the middle gear when the ABS brake modulator is mounted in the vehicle.) Is the ABS brake modulator rear gear stripped? | -- | Go to Step 18 | Go to Step 11 | ||||||||
11 |
(The ABS brake modulator rear gear is the middle gear when the ABS brake modulator is mounted in the vehicle.) Does the ABS brake modulator rear gear set move at least one full revolution in both directions? | -- | Go to Step 12 | Go to Step 17 | ||||||||
12 |
Does the ABS brake modulator rear gear rotate more than eight full turns from lock to lock? | -- | Go to Step 19 | Go to Step 13 | ||||||||
13 |
Do any of the terminals exhibit poor terminal contact or corrosion? | -- | Go to Step 20 | Go to Step 14 | ||||||||
14 |
Does DTC C1251 set as a current DTC? | -- | Go to Step 21 | Go to Step 22 | ||||||||
15 | Repair the high resistance in CKT 1284. Is the repair complete? | -- | -- | |||||||||
16 | Repair the high resistance in CKT 1285. Is the repair complete? | -- | -- | |||||||||
17 | Replace the ABS brake motor pack. Is the repair complete? | -- | -- | |||||||||
18 | Replace the ABS brake modulator gear. Is the repair complete? | -- | -- | |||||||||
19 | Replace the ABS brake modulator. Is the repair complete? | -- | -- | |||||||||
20 | Replace the terminals that exhibit signs of poor terminal contact or corrosion. Is the repair complete? | -- | -- | |||||||||
21 | Replace the EBCM/EBTCM. Is the repair complete? | -- | -- | |||||||||
22 | The malfunction is intermittent or not present at this time. Is a concern still present? | -- | Go to Diagnostic Aids |
