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

Have you checked the connectors in the wiring harnesses for the ABS unit and associated components for water intrusion or corrosion?

The codes that you've posted (details below) all point to a poor electrical connection in the circuit(s) or an open or short in the circuit(s). That could be either due to corrosion, liquid intrusion, a wiring harness rubbing against something hot or something that vibrates and has damaged the wiring.

If the wiring and connections are all intact and there are no opens, shorts to power or shorts to ground, the next think to look at would be the modules and/or sensors to make sure they're operating within spec.

U1003 Possible Causes:
*Faulty Anti-lock Brake System (ABS)
*Module Anti-lock Brake System (ABS)
*Module harness is open or shorted Anti-lock Brake System (ABS)
*Module circuit poor electrical connection

The Diagnostic Trouble Code (DTC) sets if the Anti-lock Brake System (ABS) Module fails to receive bus messages from the Dynamic Sensor for approximately 150 ms.

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C0020-1c Possible Causes:
*Faulty Anti-Lock Brake System (ABS) *Control Module Faulty Hydraulic Control Unit (HCU)
*Hydraulic Control Unit (HCU) harness is open or shorted Hydraulic Control Unit
*(HCU) circuit poor electrical connection

The Hydraulic Control Unit (HCU) consists of a valve body, pump motor, and inlet/outlets for the brake lines. The combined HCU and Antilock Brake System (ABS) module is located forward of the master cylinder.

The Anti-Lock Brake System (ABS) Module monitors the ABS Pump Motor. The ABS Module sets the OBDII code when the ABS Pump Motor is not to factory specifications.

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U0125 Possible Causes:
*Faulty Dynamics Sensor Dynamics Sensor
*Harness is open or shorted Dynamics
*Sensor circuit poor electrical connection

The Diagnostic Trouble Code (DTC) sets if the Anti-Lock Brakes System (ABS) Module fails to receive bus messages from the Dynamics Sensor.

https://repairpal.com/obd-ii-code-u0073-control-module-communication-bus-a-off

https://www.snapon.com/EN/US/Diagnostics/News-Center/CAN-Bus

https://www.obd-codes.com/u0073

I checked the first 3 and they are all Can-Bus Communication issues. Press CTRL+F and type in the code and press enter.

https://www.dtcdecode.com/Jeep

This is the last one

Jeep DTC U0212 Make: Jeep Code: U0212 Definition: Lost Communication With SCM Description: With the ignition on. Battery voltage between 10 and 16 volts. Ignition Off Draw (IOD) fuse installed. Front Control Module (FCM) is configured correctly. Bus messages not received from the Steering Control Module for approximately two to five seconds Cause:

• CAN BUS CIRCUITS OPEN OR SHORTED
• DTCS RELATED TO BATTERY VOLTAGE, IGNITION, OR VIN MESSAGES
• STEERING CONTROL MODULE POWER AND GROUND
• FCM NOT CONFIGURED CORRECTLY
• STEERING CONTROL MODULE
• MODULE THAT SET THIS DTC

..

You'll need to get a good auto electrician to look at this. The codes suggest a failed ECU, the brain reading all the engine sensors. If this fails, the car is unusable as the ECU won't let the vehicle work.
Codes read as:
U0073 - Control Module Communication Bus "A" Off
U0100 - Lost Communication With ECM/PCM "A"
U0101 - Lost Communication with TCM
U0121 - Lost Communication With Anti-Lock Brake System
(ABS) Control Module
U0155 - Lost Communication With Instrument Panel
Cluster (IPC) Control Module
I have very little experience with gearboxes so I can't really help with the 3rd gear problem.

HDM module ??????? No such module .
DTC U0100 00: Lost Communication With Engine/Powertrain Control Module (ECM/PCM)
DTC U0101 00: Lost Communication With Transmission Control Module (TCM)
DTC U0121 00: Lost Communication With Electronic Brake Control Module (EBCM)
DTC U0140 00: Lost Communication With Body Control Module (BCM)
DTC U0151 00: Lost Communication With Restraints Control Module
DTC U0155 00: Lost Communication With Instrument Panel Cluster (IPC) Control Module
DTC U0164 00: Lost Communication With HVAC Control Module
DTC U0168 00: Lost Communication With Vehicle Theft Deterrent (VTD) Control Module
DTC U0170 00: Lost Communication With Passenger Presence System (PPS)
DTC U0184 00: Lost Communication With Radio
DTC U0186 00: Lost Communication With Audio Amplifier
DTC U0194 00: Lost Communication With Digital Radio Receiver (DRR)
DTC U0198 00: Lost Communication With Communication Interface Module (OnStar®)
DTC U0209 00: Lost Communication With Heated Seat Module (HSM)
DTC U0214 00: Lost Communication With Remote Function Actuation (RFA)

These are all the modules onyour vehicle - no hdm module .

code p 0500 and 503 both refer to the vehicle speed sensor(VSS)---circuit malfunction or intermittent/ errattic high input====causes wiring-=--VSS---ECM--wiring poor connection--other connected system---instrument panel---VSS---communication control module
to have the abs light on I would be checking the communication control module or the ECM

try pulling battery for ten minutes or so and see if that clears any of the codes if not use a obd11 code reader and that should give you a correct answer

Having the vehicle checked for DTC'S - diagnostic trouble code's would be a good first step . ABS light on codes are stored . Suggest you take your vehicle to a qualified repair shop that has the knowledge an testing equipment to diagnose the problem properly .
Anti-Lock Brake System (ABS)
The 4-wheel, 4-channel anti-lock brake system (ABS) consists of the following components:

• ABS module
• Front wheel speed sensor
• Front wheel speed sensor ring (integral to the front wheel bearing)
• Hydraulic control unit (HCU)
• Rear wheel speed sensor
• Rear wheel speed sensor ring (integral to the rear halfshaft)
• Yellow ABS warning indicator
• As you can see here , it can set numerous
• DTC'S Why guess an replace parts that won't fix the problem .
• Anti-Lock Brake System (ABS) Module Diagnostic Trouble Code (DTC) Index DTC Description Source Action B1342 ECU is Faulted ABS Module NOTE: If other DTCs are present, REPAIR them before installing a new component.
  CLEAR the DTCs. RETRIEVE the DTCs. If DTC B1342 is retrieved, INSTALL a new module. REFER to Anti-Lock Brake System (ABS) Module in this section. REPEAT the self-test. B1483 Brake Pedal Input Circuit Failure ABS Module Go To Pinpoint Test B . B1676 Battery Pack Voltage Out of Range ABS Module Go To Pinpoint Test C . B2477 Module Configuration Failure ABS Module CONFIGURE the ABS module. REFER to Section 418-01 . CLEAR the DTCs. REPEAT the self-test. If DTC B2477 is retrieved again, INSTALL a new ABS module. REFER to Anti-Lock Brake System (ABS) Module . REPEAT the self-test. B2734 Pedal Travel Sensor Supply Error ABS Module Go To Pinpoint Test M . B2736 Pedal Travel Sensor Circuit Fault ABS Module Go To Pinpoint Test M . B2737 Pedal Travel Sensor Jammed Error ABS Module Go To Pinpoint Test M . B2738 Pedal Travel Sensor Velocity Error ABS Module Go To Pinpoint Test M . B2740 Pedal Travel Sensor Spike Error ABS Module Go To Pinpoint Test M . B2741 Sensor Cluster Defective ABS Module FOLLOW the diagnostic tool directions for the calibration procedure. B2900 VIN Mismatch ABS Module VERIFY that the module has the correct as-built data.
  CHECK for correct powertrain control module (PCM) and ABS module configurations using the diagnostic tool. RECONFIGURE the component as necessary. FOLLOW the diagnostic tool directions for the ABS module configuration or REFER to Section 418-01 for the PCM. CLEAR the DTC. REPEAT the self-test. C1095 ABS Hydraulic Pump Motor Circuit Failure ABS Module Go To Pinpoint Test D . C1145 Speed Wheel Sensor RF Input Circuit Failure ABS Module Go To Pinpoint Test E . C1155 Speed Wheel Sensor LF Input Circuit Failure ABS Module Go To Pinpoint Test E . C1165 Speed Wheel Sensor RR Input Circuit Failure ABS Module Go To Pinpoint Test E . C1175 Speed Wheel Sensor LR Input Circuit Failure ABS Module Go To Pinpoint Test E . C1233 Speed Wheel LF Input Signal Missing ABS Module Go To Pinpoint Test F . C1234 Speed Wheel RF Input Signal Missing ABS Module Go To Pinpoint Test F . C1235 Speed Wheel RR Input Signal Missing ABS Module Go To Pinpoint Test F . C1236 Speed Wheel LR Input Signal Missing ABS Module Go To Pinpoint Test F . C1277 Steering Wheel Angle 1 and 2 Circuit Failure ABS Module Go To Pinpoint Test G . C1278 Steering Wheel Angle 1 and 2 Signal Faulted ABS Module Go To Pinpoint Test G . C1279 Yaw Rate Sensor Circuit Failure (Sensor Cluster Fault) ABS Module Go To Pinpoint Test H . C1280 Yaw Rate Sensor Signal Fault (Sensor Cluster Fault) ABS Module Go To Pinpoint Test H . C1281 Lateral Accelerometer Circuit Failure (Sensor Cluster Fault) ABS Module Go To Pinpoint Test H . C1282 Lateral Accelerometer Signal Fault (Sensor Cluster Fault) ABS Module Go To Pinpoint Test H . C1285 Booster Solenoid Circuit Failure ABS Module Go To Pinpoint Test I . C1287 Booster Pedal Force Switch Circuit Failure ABS Module Go To Pinpoint Test J . C1288 Pressure Sensor Main/Primary Input Circuit Failure ABS Module Go To Pinpoint Test K . C1440 (with stability assist) Pressure Sensor Main/Primary Signal Faulted ABS Module Go To Pinpoint Test K . C1516 Roll Rate Sensor Signal Fault (Sensor Cluster Fault) ABS Module Go To Pinpoint Test H . C1517 Roll Rate Sensor Circuit Failure (Sensor Cluster Fault) ABS Module Go To Pinpoint Test H . C1730 Reference Voltage Out of Range (+5V) ABS Module Go To Pinpoint Test L . C1805 Mismatched PCM and/or ABS-TC Module ABS Module CHECK for correct PCM and ABS module configuration using the diagnostic tool. RECONFIGURE the component as necessary. FOLLOW the diagnostic tool directions for the ABS module configuration or REFER to Section 303-01 for the PCM. CLEAR the DTC. REPEAT the self-test. C1963 Stability Control Inhibit Warning ABS Module This DTC is for information only. GO to the Principles of Operation. CLEAR the DTC. REPEAT the self-test. C1991 Module Calibration Failure ABS Module Follow the diagnostic tool directions for the calibration procedure. C1996 Active Yaw and/or Roll Control Disabled ABS Module This DTC can be set if the ABS module system is activated for 15 seconds of continuous operation. CHECK for any major chassis modifications, gross suspension misalignment or other items that can alter the vehicle tracking dynamics. CLEAR the DTC. REPEAT the self-test. C1998 Module Calibration Not Complete ABS Module Go To Pinpoint Test O . C2769 (ABS only) Longitudinal Acceleration Sensor Electrical Failure ABS Module INSTALL a new ABS module. REFER to Anti-Lock Brake System (ABS) Module in this section. CLEAR the DTCs. REPEAT the self-test. C2769 (ABS with stability assist) Longitudinal Acceleration Sensor Electrical Failure (Sensor Cluster Fault) ABS Module Go To Pinpoint Test H . C2770 (ABS only) Longitudinal Acceleration Sensor Plausibility Failure ABS Module INSTALL a new ABS module. REFER to Anti-Lock Brake System (ABS) Module in this section. CLEAR the DTCs. REPEAT the self-test. C2770 (ABS with stability assist) Longitudinal Acceleration Sensor Plausibility Failure (Sensor Cluster Fault) ABS Module Go To Pinpoint Test H . C2777 Sensor Cluster Bus Failure (Sensor Cluster Fault) ABS Module Go To Pinpoint Test H . C2778 Sensor Cluster Power Supply Failure (Sensor Cluster Fault) ABS Module Go To Pinpoint Test H . U1900 CAN Communication Bus Fault-Receive Error Network Fault REFER to Section 418-00 . U1901 CAN Network #2 Communication Bus Fault-Receive Error Network Fault Go To Pinpoint Test H . U2023 Fault Received from External Node Instrument Cluster REFER to Section 418-00 .

B1596 ABS Module Service Continuous Codes NOTE: If other DTCs are present, REPAIR them before installing a new component.
TURN the ignition switch to the OFF position and wait at least 30 seconds. Turn the ignition switch to the ON position. REPEAT the ABS self-test. If any DTCs are retrieved, REFER to the Anti-Lock Brake System (ABS) Module Diagnostic Code (DTC) Index. If no DTCs are retrieved, CARRY OUT a drive test above 15 km/h (9 mph), then REFER to the symptom chart.
Anti-Lock Brake System (ABS) Module Diagnostic Trouble Code (DTC) Index DTCs DTC Caused By Description Action B1342 ABS Module ECU is Defective INSTALL a new ABS module. REFER to Anti-Lock Brake System (ABS) Module in this section. B1484 ABS Module Brake Pedal Input Open Circuit Go To Pinpoint Test D . B1596 ABS Module Service Continuous Codes NOTE: If other DTCs are present, REPAIR them before installing a new component.
TURN the ignition switch to the OFF position and wait at least 30 seconds. Turn the ignition switch to the ON position. REPEAT the ABS self-test. If any DTCs are retrieved, REFER to the Anti-Lock Brake System (ABS) Module Diagnostic Code (DTC) Index. If no DTCs are retrieved, CARRY OUT a drive test above 15 km/h (9 mph), then REFER to the symptom chart. B1676 ABS Module Battery Voltage Out of Range Go To Pinpoint Test E . C1145 ABS Module Speed Wheel Sensor RF Input Circuit Failure Go To Pinpoint Test B . C1155 ABS Module Speed Wheel Sensor LF Input Circuit Failure Go To Pinpoint Test B . C1165 ABS Module Speed Wheel Sensor RR Input Circuit Failure Go To Pinpoint Test B . C1175 ABS Module Speed Wheel Sensor LR Input Circuit Failure Go To Pinpoint Test B . C1222 ABS Module Speed Wheel Mismatch Make sure the tires are the same size and correctly inflated. INSPECT the wheel speed sensor rings. CLEAR the DTC. TEST drive the vehicle. REPEAT the self-test. C1266 ABS Module ABS Valve Power Relay Circuit Failure Go To Pinpoint Test K . C1296 ABS Module Wheel Speed LF Signal Fault Go To Pinpoint Test C . C1297 ABS Module Wheel Speed RF Signal Fault Go To Pinpoint Test C . C1298 ABS Module Wheel Speed RR Signal Fault Go To Pinpoint Test C . C1299 ABS Module Wheel Speed LR Signal Fault Go To Pinpoint Test C . C1300 ABS Module ABS Hydraulic Pump Motor Circuit Failure Go To Pinpoint Test A . C1805 ABS Module Mismatched PCM and ABS Modules Do Not Match CHECK the part numbers. INSTALL the correct module. C2775 ABS Module TC ON/OFF Switch Stuck Failure Go To Pinpoint Test H . U0073 CAN Bus Control Module Communication Bus Off REFER to Section 418-00 . U1900 CAN Bus CAN communication Bus Fault - Receive error REFER to Section 418-00 . U2023 CAN Bus Fault received from External Node REFER to Section 418-00 .

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


If the fault come back again, this is being caused by a failed ABS module. You will need to replace the module and run the verification process to correct your concern. To run the verification process you will need access to a full level scan tool (as factory scan).


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