U0121 : Lost Communication With Anti-Lock Brake System (ABS) Control Module

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.

U0121 est un code defaut lie a electrique, classe en gravite high. Lorsque le calculateur de ton vehicule detecte cette condition, il enregistre U0121 et allume le voyant moteur.

Si ton vehicule a declenche U0121, tu peux remarquer un ou plusieurs de ces symptomes :

• ABS, traction control, and stability control warning lights illuminated together
• Red brake warning light on some vehicles (GM trucks in particular)
• Speedometer drops to zero or reads erratically
• Hill-start assist, adaptive cruise, and lane-keep assist disabled
• Harsh or delayed transmission shifts when the TCM relies on ABS wheel-speed data
• Scan tool shows 'no communication' when trying to reach the ABS/EBCM module

Voici les causes les plus courantes de U0121 :

Non, regle ca immediatement. Standard hydraulic brakes still work, so you can limp home, but ABS, traction control, stability control, and usually hill-start assist are disabled. Avoid rain, snow, and emergency stops until it's fixed.

Suis ces etapes pour identifier la cause profonde de 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.

Les couts de reparation de U0121 varient selon la cause profonde et ton vehicule. Voici des estimations courantes :

U0121 se comporte differemment selon ton vehicule. Selectionne ta voiture ci-dessous pour des causes propres au modele, les problemes connus et des estimations de couts ajustees :

Ces codes apparaissent souvent avec U0121 ou indiquent des problemes connexes :