C0040 on Chevrolet: How to Diagnose & Fix

First-generation Avalanches (2002-2006) can experience unwanted ABS activation during normal low-speed braking. The antilock brake system activates inappropriately, causing a pulsating brake pedal and increased stopping distances when it should not be engaging. The issue is more likely in environmentally corrosive areas where corrosion builds up between the front wheel speed sensor and the hub/bearing assembly it mounts to, weakening the sensor signal. This creates a safety hazard as the vehicle takes longer to stop than expected during routine braking.

Corrosion of the front wheel-bearing hub can contaminate/affect the ABS tone ring and wheel speed sensor, causing unwanted ABS activation when braking at low speeds (roughly 3-10 mph). This extends low-speed stopping distance and pulses the pedal unexpectedly. GM issued recall 05V379000 (Aug 2005, ~1.35M vehicles) but limited the remedy largely to salt-belt states, frustrating owners elsewhere who report the same symptom.

The Express uses a sealed front hub/bearing assembly with the ABS wheel speed sensor built into the top of the unit. Two things go wrong. First, on a heavily loaded van the bearing itself wears out and produces a roar or growl that rises with road speed and changes when you sway the van side to side. Second, the seal at the ABS pickup lets water into the hub, which both destroys the bearing from the inside and corrupts the speed sensor signal - so the ABS and traction lights come on before any noise is obvious. Because the sensor is inside the hub, you cannot service the sensor separately; the whole assembly gets replaced. Owners also report a distinct pattern of ABS faults appearing right after a hub replacement when a low-cost assembly was used, which is a real and repeatable trap on this platform. GM previously recalled certain 2003 Express vans built without the wheel bearing retaining nut (NHTSA 02V305), which could allow the bearing to separate and disabled the ABS - a related but separate manufacturing defect.

The wheel speed sensors and their wiring are prone to failure due to the harsh commercial-use environment, causing the StabiliTrak and ABS systems to falsely activate during normal driving. The ABS unexpectedly engages during normal braking, extending stopping distances. The tone rings on the hub bearings also corrode.

The 2006-2013 Impala is notorious for internal breaks in the front ABS wheel-speed-sensor wiring harness. The factory routes and clamps the harness such that steering movement repeatedly flexes the wire; the copper conductors fracture inside the insulation while the outer jacket looks perfectly intact, making it hard to spot. The result is intermittent ABS, traction control, and StabiliTrak warnings — often appearing or clearing when the wheel is turned. Left front (C0035) is the most common, but both sides fail.

Colorado owners frequently report ABS warning lights, stored wheel speed sensor faults, and low-speed unwanted ABS activation, especially in rust-belt trucks. Corrosion at the front hub sensor mounting area or failing hub-integrated wheel speed sensors can create an erratic signal that the ABS module interprets as wheel slip. This issue is widely documented across GM midsize trucks and often shows up as pulsation or extended stopping distance at parking-lot speeds.

Under NHTSA recall 05V379 (GM 05068), certain 2000-2002 Suburban vehicles may experience unwanted antilock brake activation at low speed, caused by corrosion at the front wheel speed sensor mounting surface on the bearing. The condition is more likely in corrosive environments, and the recall was launched in the salt-belt states. It can increase stopping distances during low-speed braking. Only affected VINs are covered; check your VIN.

The sealed front hub bearing assemblies on the 2500HD carry heavy front axle weight, and on 4WD trucks they also carry the axle splines and the wheel speed sensor. Owners report failures well before 100,000 miles - forum reports on 2003-2005 2500HD trucks cluster between roughly 40,000 and 90,000 miles - showing up first as a humming or grinding that changes pitch when the truck is loaded into a turn, then as steering wheel vibration and play at the wheel. Because the wheel speed sensor is integrated into the hub, a failing bearing commonly turns on the ABS light and disables ABS and traction control before the noise is obvious, and a fully failed bearing can seize or allow the wheel to separate.

Silverado 1500 trucks commonly develop front hub bearing wear, especially on higher-mileage 4x4s and trucks used on rough roads or with oversized tires. Owners report a humming or growling noise that changes with speed and steering input, and because the wheel speed sensor mounts in the hub assembly, ABS and traction control warnings may appear as the bearing deteriorates. Excessive play can eventually affect braking feel and tire wear.

Front wheel hub bearings commonly fail prematurely, sometimes as early as 50,000 miles. The sealed bearing units develop excessive play and noise due to poor sealing that allows water intrusion. Road salt environments accelerate failure dramatically.

The sealed front wheel-bearing/hub assemblies wear out and produce a growing humming, rumbling, or grinding noise that changes pitch when turning or with speed. Because the wheel-speed sensor is integral to the hub, a failed bearing can also set ABS/StabiliTrak faults and light the dash. The bearing is not serviceable separately on these cars; the entire sealed hub must be replaced. Heavier wheel/tire setups and spirited driving accelerate wear.

The S-series Blazer's Kelsey-Hayes ABS system is prone to age-related faults: front wheel-speed sensors (integrated into the hub bearings) corrode and give erratic signals, the EBCM ground at the radiator support gets rusty/loose, and later Kelsey-Hayes 325 modules can fail internally. Symptoms include an ABS warning light, erratic wheel-speed codes, and in some cases the ABS pump running with the key off. Corroded grounds and connectors are a very common root cause on rust-belt trucks.