Both the ABS and brake lights are on

Welcome to 2CarPros.

That is correct. Vehicle speed and distance covered are measured by the Rear Wheel Speed Sensor. The sensor is mounted to the rear axle. A signal is sent from this sensor to the Controller Antilock Brake (CAB) computer. A signal is then sent from the CAB to the Power-train Control Module (PCM) to determine vehicle speed and distance covered. If it is failing, the symptoms you described will occur.

Here are the directions for replacement. Note that the sensor may just need cleaned or the connection may be corroded or damaged. Also, there is a tone ring in the differential that it uses to function. It could be a problem, damaged or dirty, but that is unlikely.

Here are the directions. The attached pic correlates with the directions.

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REMOVAL
1. Raise vehicle on hoist.
2. Remove brake line mounting nut and remove the brake line from the sensor stud.

Rear Speed Sensor Mounting

Pic 1


3. Remove mounting stud from the sensor and shield.
4. Remove sensor and shield from differential housing.
5. Disconnect sensor wire harness and remove sensor.

INSTALLATION
1. Connect harness to sensor. Be sure seal is securely in place between sensor and wiring connector.
2. Install O-ring on sensor (if removed).
3. Insert sensor in differential housing.
4. Install sensor shield.
5. Install the sensor mounting stud and tighten to 24 Nm (200 in. lbs.).
6. Install the brake line on the sensor stud and install the nut.
7. Lower vehicle.

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When you remove this, be careful not to break the bolt holding it in place. Once the bolt is removed, the sensor may be tight and hard to remove. Work it back and forth until it loosens. Also, clean inside where it mounts with a rag, use a new o-ring on the new sensor, and lubricate the o-ring before installing with oil.

Let me know if this helps.
Joe

Thanks Joe! When I scanned the truck last, it also popped up with a P0139 code. I assumed that was for this sensor but researching it also said it may be an O2 sensor. Is that the same thing? I haven’t replaced the speed sensor yet.

Welcome back:

No, those are two different things. The code you mentioned is for an oxygen sensor. That is mounted on the exhaust system and is part of the emissions system. The sensor on the axle is for the speed, ABS, and so on. Based on your description, either the sensor I first mentioned is bad or there is dirt causing a weak signal from the sensor.

Let me know if I can help.

Take care,
Joe