C0274Generic code

C0274 Code: Excessive Dump or Isolation Time

The C0274 code means the ABS kept the dump or isolation valves of one wheel open longer than normal, usually because it believed that wheel was locking up. The cause is more often a bad wheel sensor or tone ring than the hydraulic unit.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$20 to $900
Difficulty
Medium
System
Chassis, Brakes and Suspension
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

On this page

What the C0274 code means

The ABS module (EBCM) controls the anti-lock brakes and, on most modern vehicles, traction control and stability control too. When it detects a fault, it disables those functions and turns on the ABS and stability warning lights. The normal brakes keep working.

During an ABS stop, the module opens and closes valves to release pressure at the wheel that is locking. If that cycle lasts too long, it stores the C0274 code and shuts the ABS off for safety.

The cause is usually a false locked wheel signal, from a wheel sensor or a toothed ring in poor condition, rather than a fault in the hydraulic unit.

Important: many C and B codes are not generic. The definition on this page is the most widespread one, used by General Motors and most generic scan tools, but on other makes the same number can mean something else. Always confirm the code text with a scan tool that reads the right module (ABS, body or airbag).

So when you see the C0274 code, start with the wheel speed sensors and rings, and check for wheel sensor codes that often come along with it. Replacing the hydraulic unit should be the last step, and only if the tests confirm it.

C0274 code symptoms

  • ABS warning light on.
  • The ABS kicks in at low speed for no reason.
  • Brake pedal that pulses as you come to a stop.

Likely causes of the C0274 code

  1. Wheel sensor or toothed ring. It gives a false lockup signal.
  2. Rust or dirt on the ring. Confirm it with the tests in the diagnosis section.
  3. Hydraulic unit valves with an internal fault. Uncommon.
  4. Worn brakes that lock a wheel.

How to diagnose the C0274 code step by step

  1. Check for wheel sensor codes. They often come with this one.
  2. Compare the wheel speeds during a gentle stop.
  3. Inspect the sensors and rings.
  4. Check the condition of the brakes.

How to fix the C0274 code

  • Repair the affected sensor or ring.
  • Check the pads, rotors and calipers.
  • Replace the hydraulic unit only if the tests confirm it.

Technical reference data

  • The dump valves work in cycles of milliseconds during an ABS stop.
  • These values are approximate. Check the manufacturer data for your vehicle.

Brand-specific notes

Rusty tone rings and worn sensors are the usual suspects, so inspect them before you consider anything hydraulic.

C0274 on Chevrolet and GMC

This code is common on the Chevrolet Silverado, the GMC Sierra and the Chevrolet Tahoe.

Frequently asked questions about C0274

What does the C0274 code mean?
It means the ABS held the dump or isolation valves of a wheel open longer than normal, usually because it thought that wheel was locking up.
Can I drive with a C0274 code?
Yes, with caution. The C0274 code leaves the normal brakes working, but without ABS or stability control. Leave extra stopping distance on wet roads.
Is it the hydraulic unit?
Rarely. Almost always it is a false wheel signal.
Why does the pedal pulse when I stop?
Because the ABS acts when it should not, due to the wrong signal.
How much does it cost to fix C0274?
Roughly between $20 and $900. A cleaned sensor is at the low end, and a hydraulic unit is at the high end.
Will a C0274 code clear itself?
Only if the false signal was temporary, such as dirt that came loose. A rusty ring or a worn sensor will bring it back.

Related codes

Questions about the C0274 code

There are no questions about this code yet. Tell us about your case: vehicle, symptoms and what you have already checked.