C0040 explained: Right rear sensor signal is missing or out of range. Sensor failure is most common, but on solid axles a damaged exciter ring in the differential is also a frequent cause.
🎯 Top Causes & Probability
50%
#1 - Most Likely
Failed Rear Wheel Speed Sensor
Sensor seizes in its bore from rust or cracks internally. Heat and de-icer accelerate failure.
🔨 Part
$30-$130
👨🔧 Labor
$60-$160
⚡ DIY
Easy
28%
#2 - Check First
Damaged or Loose Exciter Ring
On solid axles the tone ring is pressed onto the axle. Wheel bearing play or a strike can knock teeth off.
🔨 Part
$80-$300
👨🔧 Labor
$220-$520
⚡ DIY
Hard
16%
#3 - Less Common
Wiring Harness Issues
Rear sensor wire routes near the suspension and sees water spray. Open circuits or shorts to ground are common.
🔨 Part
$10-$60
👨🔧 Labor
$80-$160
⚡ DIY
Medium
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Read live wheel speed data while driving. Right rear dropping to zero or noisy is the signature.
- Inspect the sensor wire from the differential to the body harness for rub-throughs.
- Pull the sensor and check for metal debris stuck to the tip.
- On solid axles, pull the inspection cover and check the tone ring teeth on the carrier.
- Replace sensor, ring, or repair the harness as the inspection indicates.
❓ Frequently Asked Questions
Why is my truck pulling C0040 after a brake job?
A pry bar slipped against the tone ring during caliper removal, or a sensor wire was knocked loose. Recheck your work.
Can a bad rear wheel bearing trigger C0040?
Yes. Bearing slop lets the tone ring wobble out of the sensor gap.
Is the rear sensor a hub assembly?
On many trucks, no, it is a separate sensor that bolts into the axle or backing plate. Check your specific year and make.
Will this trigger an ABS lamp only or also the stability lamp?
Both. Loss of a wheel speed disables ABS, traction, and stability control.