Case IH 12628 – ABS / Brake Control Module or Transmission / Drivetrain ECU: Rear left wheel speed sensor - air gap (no signal)

The control module is not receiving a valid speed signal from the rear left wheel speed sensor. The system specifically flags the 'air gap,' indicating that the physical distance between the sensor tip and the tone ring (reluctor wheel) is likely out of specification, or the sensor has failed completely, resulting in a 'no signal' condition.

• Magnum
• Puma
• Maxxum
• T-series

1. 1

   Inspect the mounting of the rear left wheel speed sensor to ensure it is sitting completely flush against its mounting surface. Look for rust or dirt buildup under the flange that could increase the air gap.

2. 2

   Remove the sensor and inspect the tip for a buildup of ferrous material (metal shavings), thick grease, or mud that can block the magnetic signal.

3. 3

   Look through the sensor mounting hole while slowly rotating the wheel to verify that the tone ring teeth are not damaged, missing, or heavily corroded.

4. 4

   Inspect the sensor's pigtail connector and the main machine wiring harness for corrosion, moisture, or backed-out pins.

5. 5

   Using a multimeter or oscilloscope, back-probe the sensor connector while rotating the rear left wheel to check for a pulsing signal (square wave or AC voltage). If no signal is generated but wiring is intact, the sensor is dead.

1. 1

   Preparation

   Park the tractor on level ground, turn the ignition OFF, apply the parking brake, and securely chock the wheels.

2. 2

   Locate the Sensor

   Locate the rear left wheel speed sensor on the rear axle housing or wheel hub assembly.

3. 3

   Disconnect

   Unplug the electrical connector from the sensor harness.

4. 4

   Removal

   Remove the single retaining bolt securing the sensor to the housing. Carefully twist and pull the sensor out of the bore.

5. 5

   Clean the Port

   Thoroughly clean the mounting surface and the bore hole. Any rust or debris left on the mounting pad will alter the air gap of the new sensor and cause the 12628 code to return.

6. 6

   Installation

   Insert the new wheel speed sensor into the bore. Ensure it sits completely flush against the machined surface.

7. 7

   Secure

   Install and tighten the retaining bolt to the manufacturer's specified torque (do not overtighten, as this can crack the plastic sensor housing).

8. 8

   Reconnect & Clear

   Reconnect the electrical harness. Power on the machine, use a diagnostic scan tool to clear the 12628 fault code, and test drive the tractor above 10 km/h to verify the ECU is reading the rear left wheel speed accurately.