U0248 Lost communication with remote accessory module

OBD-II DTC Datasheet

Lost Communication With Remote Accessory 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 Remote Accessory Module (RAM) and other control modules on the vehicle are not communicating 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 Remote Accessory Module (RAM) is usually located behind the dashboard on either side of the vehicle. Can also be installed inside the center console. 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 control the actuation of any remotely controlled device on the vehicle that is not currently controlled by another system. This gives the manufacturer the ability to diagnose and troubleshoot these often overlooked / add-on systems.

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 seriousness in this case is never serious, as this is a device for the convenience of customers, and in the event of a complete power failure, there is always a manual workaround. The lack of work of the RAM does not in any way affect the operation of the car.

Symptoms of a U0248 code may include:

Remote controlled accessories do not move / do not work / do not turn on / do not light up
RAM 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 the RAM 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 U0248 code before any of the underlying codes are thoroughly diagnosed and corrected.

If the only code you are getting from other modules is U0248, try accessing the RAM. If you can access codes from RAM then code U0248 is either intermittent or memory code. If the RAM cannot be accessed, then code U0248 set by other modules 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 remote accessory module.

Check all fuses supplying the RAM module on this vehicle. Check all bases for RAM. Locate grounding attachment 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 RAM module. If RAM connectivity recovers, the problem is most likely related to fuses / connections.

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 RAM connector, which is usually located behind the dashboard, on either side of the vehicle. can also be installed inside the center console. Disconnect the negative battery cable before disconnecting the RAM connector. 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 RAM. You will need access to a digital volt/ohmmeter (DVOM). Make sure you have power and ground on the RAM. Access the wiring diagram and determine where the main power and ground sources enter the RAM. Connect the battery before continuing with the RAM disabled. Connect the red lead of your voltmeter to each B+ (battery voltage) power supply going into the RAM 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 U0248, the only thing to do is to seek help from a trained automotive diagnostician, as this will indicate a RAM failure. Most of these RAMs must be programmed or calibrated in order to properly install the car.

Related DTC discussions

There are currently no related topics in our forums. Post a new topic on the forum now.

Need more help with the U0248 code?

If you still need help with DTC U0248, post a question in the comments below this article.

NOTE. This information is provided for informational purposes only. It is not intended to be used as a repair recommendation and we are not responsible for any action you take on any vehicle. All information on this site is protected by copyright.