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DTC/U0121·Chevrolet

U0121 on Chevrolet: Causes, Symptoms and Fix Cost

Quick Answer
High SeverityNot safe to driveChevrolet

U0121 on a Chevrolet means another module (usually the PCM or gateway) can no longer talk to the ABS control module over the CAN bus. ABS, traction control, and ESC are disabled until the fault is repaired.

Repair cost on Chevrolet€32 - €1750

What does U0121 mean on a Chevrolet?

U0121 means another module (usually the PCM or gateway) can no longer talk to the ABS control module over the CAN bus. ABS, traction control, and ESC are disabled until the fault is repaired.

Chevrolet Silverado 1500

2007-2013 (GMT900, 5.3L Vortec)

EBCM failures on GMT900 trucks are so common that GM issued Special Coverage 14882 on some VINs. Speedometer drops to zero alongside U0121 is the tell-tale sign.

What causes U0121 on a Chevrolet?

Beyond the generic causes listed on the main U0121 page, these are the Chevrolet-specific patterns we see most often:

Chevrolet Silverado 1500Internal EBCM failure (Kelsey-Hayes 325 unit)
Chevrolet Silverado 1500Corroded G200 ground behind the left cylinder head

How to diagnose U0121 on a Chevrolet with OBD2

Follow these steps to pinpoint the root cause of U0121:

  1. Scan every module on the vehicle, not just the PCM. If only the ABS module fails to respond, the fault is localized to it, its wiring, or its power supply.
  2. Load-test or replace the battery first. Below about 11.5V many modules drop off the CAN bus and throw U-codes that mimic hardware failure.
  3. Pull the ABS fuse(s) per the wiring diagram and confirm continuity. Check any dedicated ABS relay in the underhood fuse box.
  4. Unplug the ABS module and inspect the connector for green corrosion, water, or backed-out pins. On trucks and SUVs this is by far the most common find.
  5. Back-probe the connector with the key on: verify battery voltage on the power pin(s) and less than 0.1V drop from the module ground pin to battery negative.
  6. Measure resistance across DLC pins 6 and 14 with the key off. You should see roughly 60 ohms. 120 ohms means one terminating resistor is missing (broken bus wire); much lower means a short.
  7. Scope CAN High and CAN Low at the ABS connector. No traffic with good power and ground confirms broken wiring between the module and the gateway.
  8. If power, ground, and CAN traffic are all present at the connector and the module still won't answer, replace or refurbish the module and code it to the vehicle.

How much does U0121 cost to fix on a Chevrolet? (EUR)

Estimated repair costs on a Chevrolet (Chevrolet costs align with the average for this code across makes).

Repair Parts Cost Labor Cost Total Estimate DIY Difficulty
Diagnostic scan and CAN bus test at an independent shop €0–€0 €60–€150 €60–€150 Moderate
Repair corroded ABS connector or replace pins €10–€60 €80–€250 €90–€310 Moderate
Replace ABS fuse or repair power/ground circuit €2–€30 €30–€120 €32–€150 Easy
Replace ABS control module (new, coded to VIN) €400–€1400 €100–€350 €500–€1750 Professional
Mail-in refurbishment of existing ABS module (BBA Reman, ECU Testing) €150–€400 €80–€200 €230–€600 Professional

Prices estimated as of May 2026. Costs vary by region, vehicle, and shop.

These codes commonly cluster with U0121 on Chevrolet vehicles:

U0100ChevroletU0101U0073U0140C0800

FAQ: U0121 on Chevrolet

My speedometer stopped working at the same time as the ABS light came on. Are they related?

Yes, and it's a classic U0121 symptom on GM trucks and many European cars. The cluster reads vehicle speed from the ABS module over CAN. When the ABS module drops off the bus, the speedo has no signal and reads zero.

Why did U0121 appear right after I jump-started or replaced my battery?

Voltage dips during a sloppy jump-start can latch communication faults in modules that are sensitive to under-voltage. Disconnect the battery for 15 minutes, reconnect cleanly, and clear the code. If it returns within a drive cycle, you have a real wiring or module fault.

Will U0121 fail an MOT or periodic inspection?

Yes. An illuminated ABS warning lamp is an automatic MOT fail in the UK and a major defect on EU roadworthiness inspections since Directive 2014/45/EU.

Can I fit a used ABS module from a scrapyard?

Sometimes on pre-2010 cars, but most modern modules are VIN-locked. On VAG, BMW, and FCA vehicles a used unit needs dealer or specialist programming (ODIS, ISTA, wiTech) before it'll communicate. Refurbishment of your original is usually cheaper and plug-and-play.

Could a bad wheel speed sensor set U0121?

No. Wheel speed sensor faults set C-codes like C0035 through C0050. U0121 is strictly about the CAN link to the ABS module itself.

Looking for the full U0121 reference (all makes, full diagnosis flow, complete repair cost matrix)?

See the main U0121 guide
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