So you should chech it on our car models. U if your catalytic convertor fails completely, you eventually won't be able to keep the car running. Your gas mileage will also be terrible, so you should try and fix it as soon as you can.

What Does the Electronic Stability Control (ESC) Warning Light Mean?

Is the fuel pump sometimes not priming when you turn the key to ON II? Start by measuring the fuel pressure and checking whether you have bright white-bluish spark at all four plugs.

The mechanical timing is also something that you should check, as we mentioned above. U DTC specifically refers to the camshaft cam timing. In this case, if the cam timing is over-retarded, the engine light will be illluminated and the code will be set. Engine trouble codes resource center for all car models. Code Search Please fill the "Code Box" to find engine fault code. Select Abadal Schneider Th. Clubsport Yes! Ways to read engine trouble codes.

Ways to clear check engine light on car panel. Check Engine Light Dictionary Ways to clear check engine light on car panel. Operating information and comm U code.Welcome to world's most trustworthy automotive forum. Thread Rating: 19 Vote s - 2.

Mercedes x GLC front crash some xentry fault help. Reputation: 4. Edit Reason: google search. Hello, I am working on a x front crash, all front as been changed and still some faults in xentry. Can you tell me what do you think it can be? Xentry rapport in attachment. Engine runing now unlocked with xentry front bumper not mounted yet.

Airbags faults are normal ordered airbags from Mercedes and waiting for them before remplace. P The outside temperature sensor has an electrical fault. There is a signal below the permissible limit value. UB87 Communication with the control unit 'Headlamp' has a malfunction.

The message is missing. The actuator is blocked. There is a short circuit to ground. Thank you for your ideas. I think, in the car condition a diagnosis would be premature. First, assemble everything Reputation: The only suggestion to question like that - press on fault code and do guided test.

My old contributions are not password protected. Get them if you need them. I will delete them in order to make space for new ones. I have the same faults with headlights on wDe browser ondersteunt geen in line frames of is momenteel zodanig geconfigureerd dat in line frames niet kunnen worden weergegeven.

For contactremarksinfo or suggestions:. Important notice :. All mentioned names and rights belong to the owner. Disclaimer: The opinions expressed here represent the opinions of the author and not necessarily those of www. All data and information provided in this article is for informational purposes only. All information is provided on an as-is basis. M ercedes Fault codes can be a pain especially the body and chassis control codes.

Here is a detailed list of them:.

U0121 - Lost Communication With Anti-Lock Brake System Control Module

Air bag signal will cause the engine stop. Radiator shutter regulator fault via ground key. Circuit open P check M44 booster air cooler circulation pump.

mercedes u012100

Short to ground P check M44 booster air cooler circulation pump. Short P charging pressure too low. P check anti-theft lock. P check N73 controller EIS.

mercedes u012100

Sensor 1 signal voltage too high. P check B37 accelerator pedal position sensor. Sensor 1 signal voltage too low. Sensor 2 signal voltage too high. Sensor 2 signal voltage too low. Cannot receive all CAN information. P large external interference from EGS. CAN-signal implausible. Request information of controller EGS implausible.

P large external interference from ESP. No communication P large external interference from ESP. Request of controller DTR implausible.We recommend Torque Pro. In essence, this system monitors output data from all control modules involved in the operation of the vehicle, and it can be likened to a computer network that monitors operational systems in a complex, automated manufacturing environment where several controllers work together to deliver a final product.

mercedes u012100

In this case, the final product is the safe and efficient operation of the vehicle. In practical terms, the GMLAN system is a sort of clearing house for all information exchanged between the various modules that control systems like the ABS brakes and associated safety systems like Traction and Stability Controlthe transmission, fuel management, and others.

Moreover, the GMLAN system supervises communication between the various control modules, each of which contains prerecorded information about the type s of signals that need to be exchanged between them to ensure efficient and trouble free operation of the vehicle.

In addition, the PCM expects to receive regular availability, or status, reports from each control module in the system.

In the case of the ABS control module, an interruption of more than milliseconds will set the code, since an interruption in communication can affect associated systems like Traction and Stability Control, since these safety systems share some of the circuitry and functionalities of the ABS system. To facilitate fault diagnosis, each availability report contains a unique code that identifies the control module that sends the report, thus enabling the PCM to identify defective modules correctly.

The image below shows a typical ABS actuator with the control module contained in the black plastic box. Note the pins in the connector; on this particular unit the ABS brakes, Electronic Traction Control, and Electronic Stability Control share the control module, hence the large number of pins in the connector.

Note that this example is only representative of ABS actuators, and that designs, locations, and functionalities differ widely between applications. The possible causes of the failure of the ABS control module or any other controller for that matter are many and varied, including some causes not related to the ABS circuit at all.

Below are some possible causes of code U In some cases, replacement of other, unrelated control modules such as transmission control modules can lead to a loss of communication, and hence the setting of code U Voltage spikes due to incorrect jump starting procedures or other causes can damage one or more controllers, including the ABS control module. On some vehicles, most notably many Mazda products, this code can sometimes be set if a scanner or code reader is connected while the engine is running or the ignition is switched on.

Low battery voltages or defective batteries can cause sporadic faults throughout the electrical system, and it can even damage some controllers, including the ABS control module. Note that where low battery voltages or defective batteries are involved, other codes will usually be present along with U Failed, or failing PCM.

On some applications there may be no outward signs of trouble apart from the presence of code U, and an illuminated warning light. However, some applications can display severe symptoms, but note that not all symptoms will be present on all applications all of the time. Moreover, the severity of some symptoms may differ between applications. Some common symptoms of code U could include the following. WARNING: Apart from a wiring diagram, a good quality digital multimeterand sometimes an oscilloscope, diagnosing code U requires specialist knowledge of the application being worked on, as well as above average knowledge of automotive electronics and diagnostic procedures.

Diagnosing this code is therefore not recommended for persons who do not possess these skills. NOTE 1: While most repair manuals will assist in locating the various control modules, they will rarely contain information on how to test a particular module.

Therefore, unless the manual clearly describes testing procedures for a particular control module, do NOT attempt to open or repair a suspected defective module. NOTE 2: In most cases, the repair procedure for code U is make and model specific, since the replacement module sometimes needs to be integrated with, or matched to the PCM.

While it is sometimes possible to do this on a DIY basis, it is recommended that this step be performed by a dealer or specialist repair shop that has the required equipment to verify that the integration is successful. Record all fault codes present, as well as all available freeze frame data.ABS only activates when you step on the brake pedal, but what about the rest of the time?

Like the anti-lock braking system, the ESC system monitors the rotational speed of the wheels and other parameters such as steering angle. There are many names for electronic stability control, such as vehicle stability control VSC and dynamic stability control DSCbut they all perform similar functions. It is important to understand how your particular control system works because the ESC light on the dash could have multiple meanings. Generally, the light will illuminate when the computer is actively trying to maintain traction control.

This light will stay lit only while the vehicle is not under control. If the light stays on constantly, it is likely that a malfunction has been detected or the system has been shut off manually. If a malfunction has been detected, the system will be deactivated temporarily until it is remedied. Try to keep the light off as much as possible. If you are driving in slippery conditions and the light keeps illuminating, slow down so the car is easier to control. Any issues preventing the stability control from operating should be addressed as soon as possible too.

There are times when you need to turn the stability control off, but you can leave it on for the most part. The most popular service booked by readers of this article is Warning Light is on Inspection. Our certified mobile mechanics make house calls in over 2, U. Fast, free online quotes for your car repair. Schedule Warning Light is on Inspection. Service Area.

Average rating from customers who received a Warning Light is on Inspection. What the ESC light means It is important to understand how your particular control system works because the ESC light on the dash could have multiple meanings.

Is it safe to drive with the ESC light on? Home Articles. The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details.

OBD II Fault Code P042F :

Related Articles. Related Questions. Transmission temperature indicator light randomly comes on and off but transmission is fine. Hey there, thanks for writing in about your Dodge Dakota. You may have a defective transmission temperature sensor in the transmission pan that needs to be replaced. This is a common problem that can trigger the transmission temperature indicator Glow light flashes always The glow plug Warning Light on your vehicle not only indicates that the glow plugs are operating, but also acts as a malfunction indicator lamp MIL for the engine management system.

An on-site diagnosis will be required by a mechanic What does the lamps on reminder light mean? The lamps on reminder light is located on the instrument panel.

When the lamps on reminder light is illuminated, that means that your lights are currently on. When you turn off all of your lights, the lamps on reminder light Recent Warning Light is on Inspection reviews. Excellent Rating. Average Rating 4. Number of Reviews Rating Summary.We recommend Torque Pro. Note that code U is also sometimes further defined by a sub-code in this manner — U In these cases, the sub-code serves to define the particular system in which the fault is present.

However, since not all manufacturers employ sub-codes, always refer to the manual for the affected application to determine the exact definition of code U as it applies to that particular application. In general terms though, all control modules on a modern application are interconnected via a highly complex web of wiring harnesses that is collectively known as the CAN Controller Area Network bus system.

Due to the highly complex nature of modern CAN bus systems the fault can be located almost anywhere in the CAN bus system. However, depending on the application, other systems may be involved or implicated, so always refer to the manual for the application for details on the most likely fault locations, or the location of control modules that may have failed. Although the most symptoms of code U are largely make and model specific, some common symptoms could include the following.

NOTE: Refer to the manual for the affected application for detailed information on the symptoms that are most likely to be present on that application. NOTE: Replacing control modules may sometimes require reprogramming of the replacement module, or integration of the replacement module into the CAN bus system to allow the PCM to recognize the replacement module. Failure to perform the reprogramming or integration process may result in a recurrence of the problem, or an inability to clear the code.

Code Ushould be considered as serious since in some cases, the vehicle could enter a fail-safe or limp mode.

U0121 – Data bus: anti-lock brake system (ABS) control module – no communication

It is sometimes possible to diagnose and repair code U on a DIY basis; however, in most cases, diagnosing code U requires the use of advanced, make-and-model specific diagnostic equipment, as well as above average diagnostic skills.

Note that cheap, generic code readers are generally not able to diagnose CAN bus, or control module related codes. If suitable diagnostic equipment is not available, refer the vehicle to the dealer or other specialist repair facility for professional diagnosis and repair. One other common mistake many mechanics make is not investigating and resolving codes that accompany U For instance, codes that indicate low system voltages are often ignored, even though these codes are often the direct cause of U Failure to make proper reference to the manual WILL lead to misdiagnoses, wasted time, and the unnecessary replacement of expensive parts and components that could include control modules.

Record all fault codes present, as well as all available freeze frame data. This information could be of use should an intermittent fault be diagnosed later on. NOTE: If other codes are present, make a careful note of the order in which they were stored, since resolving codes that precede U in this order will sometimes resolve U as well.Visually inspect the related wiring harness and connectors.

Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.

Mercedes C220 W204 ABS Traction Control Lights On

Cost of diagnosing the U code Labor: 1. The auto repair labor rates vary widely across the country, and even within the same city. Operating information and commands are exchanged among the devices. The devices have programmed information about what messages are needed to be exchanged on the serial data circuits.

CAN bus uses two dedicated wires for communication. When the CAN bus is in idle mode, both lines carry 2. When data bits are being transmitted, the CAN high line goes to 3. Since communication relies on a voltage differential between the two bus lines, the CAN bus is NOT sensitive to inductive spikes, electrical fields, or other noise. Pictures shown may vary from actual. U More Information Need more information on how to fix the U code?

Get Access to Factory Service Manuals. Related Information. Repair Importance Level: 3. Why is the Engine Light ON?


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