U0234 Lost communication with convenience call module

OBD-II DTC Datasheet

Lost connection with the “Convenient feedback” module

What does this mean?

This is a generic communications system diagnostic trouble code that applies to most makes and models of OBD-II vehicles.

This code means that the Convenient Recall Module (CRM) and other control modules on the vehicle do not interact with each other. The circuitry most commonly used for communication is known as Controller Area Bus communication, or simply the CAN bus.

Modules communicate with each other over a network, just like the network you have at home or work. Car manufacturers use several networked systems. Prior to 2004, the most common (non-exhaustive) inter-module communication systems were the serial communication interface, or SCI; SAE J1850 or PCI bus; and Chrysler Collision Detection, or CCD. The most common system used after 2004 is known as Controller Area Network communication, or simply the CAN bus (also used until 2004 on a small segment of vehicles). Without this CAN bus, control modules cannot communicate and your scan tool may or may not receive information from the vehicle, depending on which circuit is affected.

The Comfort Recall Module (CRM) is usually located behind the dash in the center of the vehicle. Installation under / inside the center console is possible. It receives input from a variety of sensors, some of which are directly connected to it, and most are transmitted over a bus communication system from the powertrain control module (PCM). These inputs allow the module to determine when legacy control modules on the vehicle will be updated.

Troubleshooting steps may vary depending on the manufacturer, the type of communication system, the number of wires, and the colors of the wires in the communication system.

Code severity and symptoms

The severity in this case may or may not be serious, depending on which module needs to be updated. The manufacturer may provide a workaround / workaround until the module is updated. Lack of CRM operation may or may not affect vehicle performance.

Symptoms of a U0234 code may include:

Malfunction Indicator Light (MIL) is on
Depending on the module to be updated, all of the indicator lights associated with that module will be on or blinking.
CRM does not turn on / does not work

reasons

Usually the reason for installing this code is:

Open on CAN bus + or - circuit
Short to ground or ground in any CAN bus circuit
No power or ground to CRM module
Rarely - the control module is faulty

Diagnostic and repair procedures

A good place to start with ALL electrical diagnostics is to check the Technical Service Bulletins (TSB) for your vehicle. The problem you are facing may be known to others in the field. A known fix may have been released by the manufacturer and can save you time and money during diagnostics.

It is assumed that you have access to a code reader at this point, as you may have been able to access the codes up until now. See if there were any other DTCs related to bus communication or battery / ignition. If so, you should diagnose them first, as misdiagnosis is known to occur if you diagnose the U0234 code before any of the underlying codes are thoroughly diagnosed and corrected.

If the only code you get from other modules is U0234, try accessing CRM. If you can access codes from CRM, then code U0234 is either intermittent or memory code. If you cannot access the CRM, then the U0234 code that other modules install is active and the problem already exists.

The most common failure is a circuit failure that results in a loss of power or ground to the convenience recall module.

Check all fuses supplying the CRM on this vehicle. Check all the reasons for CRM. Locate ground anchorage points on the vehicle and make sure these connections are clean and secure. If necessary, remove them, take a small wire bristle brush and baking soda / water solution and clean each one, both the connector and the place where it connects.

If any repairs have been made, clear the diagnostic trouble codes from any modules that set the code in memory and see if you can now communicate with the CRM module. If CRM connectivity is restored, the problem is most likely a fuse / connection issue.

If the code returns or communication with the module still cannot be established, locate the CAN bus communication connections on your vehicle, most importantly the CRM connector, which is usually located behind the dashboard, in the center of the vehicle. possibly installed under / inside the center console. Disconnect the negative battery cable before disconnecting the connector from the CRM. Once detected, visually inspect the connectors and wiring. Look for scratches, scuffs, exposed wires, burn marks, or molten plastic.

Disconnect the connectors and carefully inspect the terminals (metal parts) inside the connectors. See if they look burnt or have a green tint indicating corrosion. If you need to clean the terminals, use an electrical contact cleaner and a plastic bristle brush. Allow to dry and apply electrical grease where the terminals touch.

Perform these few voltage checks before connecting the connectors back to the CRM. You will need access to a digital volt/ohmmeter (DVOM). Make sure the CRM has power and ground. Access the wiring diagram and determine where the main power and ground sources enter the CRM. Reconnect the battery before continuing with CRM still disabled. Connect the red lead of your voltmeter to each B+ (battery voltage) power supply going into the CRM connector, and the black lead of your voltmeter to a good ground (if you're not sure, battery negative always works). You should see the battery voltage reading. Make sure you have a good reason. Connect the red lead of the voltmeter to the battery positive (B+) and the black lead to each ground circuit. Once again, you should see the battery voltage every time you connect. If not, repair the power or ground circuit.

Then check the two communication circuits. Locate CAN C+ (or HSCAN+) and CAN C- (or HSCAN - circuit). With the black wire of the voltmeter connected to a good ground, connect the red wire to CAN C+. With the key on and engine off, you should see about 2.6 volts with little fluctuation. Then connect the red wire of the voltmeter to the CAN C- circuit. You should see about 2.4 volts with little fluctuation. Other manufacturers show CAN C- at about 5V and an oscillating key with the engine off. Check your manufacturer's specifications.

If all tests pass and communication is still not possible, or you were unable to reset DTC U0234, the only thing to do is to seek help from a trained automotive diagnostician, as this will indicate a CRM failure. Most of these CRMs must be programmed or calibrated in order to properly install the vehicle.

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