U0100 - Lost Communication With ECM / PCM "A"

OBD-II DTC Datasheet

U0100 - Lost communication with ECM / PCM "A"

What does code U0100 mean?

This is a generic network communication code which means it covers all brands / models from 1996 onwards. However, specific troubleshooting steps may differ from vehicle to vehicle.

Generic OBD Trouble Code U0100 is a serious situation where the signals between the electronic control module (ECM) or powertrain control module (PCM) and a specific module have been lost. There may also be a problem with the CAN bus wiring that is interfering with communication.

The car will simply shut down at any time and will not restart while the connection is interrupted. Almost everything in modern cars is computer controlled. The engine and transmission are completely controlled by the computer network, its modules and actuators.

The U0100 code is generic because it has the same frame of reference for all vehicles. Somewhere on the CAN bus (Controller Area Network), an electrical connector, wiring harness, module has failed, or a computer crashed.

The CAN bus allows microcontrollers and modules, as well as other devices, to exchange data independently of the host computer. The CAN bus was developed specifically for cars.

U0100

Symptoms of the OBD2 error code - U0100

Before moving on, let's look at the main symptoms of the U0100 code.

Let's start with what we already mentioned: the check engine light or all of your vehicle's warning lights come on at the same time. But there are other things that can also indicate the appearance of the code U0100.

Symptoms of DTC U0100 may include.

• The car stalls, won't start, and won't start
• OBD DTC U0100 will set and the check engine light will illuminate.
• A car can start after a period of inactivity, but its operation is risky as it can fail again at the most inopportune moment.

All of these problems stem from the same cause: a problem with your vehicle's power management module (PCM). The PCM controls a wide range of systems in your vehicle, including air/fuel ratio, engine timing, and the starter motor. It's connected to dozens of sensors in your car, from tire pressure to intake air temperature.

Possible reasons

This is not a common problem. In my experience, the most likely problem is the ECM, PCM, or transmission control module. The car has at least two places for the CAN bus. They may be under the carpet, behind the side panels, under the driver's seat, under the dashboard, or between the A/C housing and the center console. They provide communication for all modules.

Failure of communication between anything on the network will trigger this code. If additional codes are present to localize the problem, the diagnosis is simplified.

The installation of computer chips or performance enhancing devices may not be compatible with ECM or CAN bus wiring, resulting in loss of the communication code.

A bent or extended contact lug in one of the connectors, or poor grounding of the computer will trigger this code. A low battery bounce and an unintentional polarity reversal will momentarily damage the computer.

The following are a few of the most common causes of DTC U0100.

• Faulty ECM , TCM or other network modules
• "Open" wiring in the CAN-bus network
• Ground or short circuit in the CAN bus network
• Contact defect associated with one or more CAN bus network connectors.

How serious is the U0100 code?

DTC U0100 is usually considered extremely serious . This is because such a condition may cause the vehicle to stop accidentally or may prevent the vehicle from starting, thus leaving the unfortunate motorist stranded.

In most cases, immediate diagnosis and resolution of the root cause of DTC U0100 will be required, as this will seriously impede driving. If this sort of problem only comes up to seemingly fix yourself, don't give in to a false sense of security. This problem will almost certainly recur when you least expect it.

In either case, the root cause of DTC U0100 must be diagnosed and repaired as soon as possible. This prevents the risk of a dangerous stop or getting stuck. If you are not comfortable dealing with such problems yourself, make an appointment with a reliable service center as soon as possible.

Diagnostic and repair procedures

Search the Internet for all service bulletins for your vehicle. Check bulletins for references to U0100 and suggested repair procedure. While online, check to see if any reviews have been posted for this code and check the warranty period.

Diagnosing and fixing these kinds of problems is difficult at best with proper diagnostic equipment. If the problem appears to be a faulty ECM or ECM, it is highly likely that programming will be required before starting the vehicle.

Please refer to your service manual for a detailed description of the additional code associated with the faulty module and its location. Look at the wiring diagram and find the CAN bus for this module and its location.

There are at least two places for the CAN bus. Depending on the manufacturer, they can be located anywhere inside the car - under the carpet near the sill, under the seat, behind the dash, in front of the center console (console removal required), or behind the passenger airbag. CAN bus access.

The location of the module depends on what it is working with. The airbag modules will be located inside the door panel or under the carpet towards the center of the vehicle. Rocker modules are usually found under the seat, in the console, or in the trunk. All later car models have 18 or more modules. Each CAN bus provides communication between the ECM and at least 9 modules.

Refer to the service manual and locate the contacts of the corresponding module. Disconnect the connector and check each wire for a short to ground. If a short is present, instead of replacing the entire harness, cut the shorted wire from the circuit about one inch from either connector and run an equivalent sized wire as an overlay.

Disconnect the module and check the associated wires for continuity. If there are no breaks, replace the module.

If there were no additional codes, we are talking about ECM. Install a memory saver device before unplugging anything to save ECM programming. Treat this diagnosis in the same way. If the CAN bus is good, the ECM must be replaced. In most cases, the car must be programmed to accept the key and the program installed in the computer for its operation.

Have the vehicle towed to the dealer if necessary. The least costly way to fix this type of problem is to find an auto shop with an older, experienced ASE automotive technician with the proper diagnostic equipment.

An experienced technician is usually able to quickly identify and fix a problem in less time at a more reasonable cost. The reasoning is based on the fact that the dealer as well as independent parties charge hourly rates.

💥 U0100 | OBD2 CODE | SOLUTION FOR ALL BRANDS

Instructions for troubleshooting error U0100

The following steps can be used to diagnose and resolve the root cause of a vehicle's DTC U0100. As always, before proceeding with such repairs, you should also familiarize yourself with factory service manual for a specific make and model of vehicle.

1 - Check for additional trouble codes

Before starting the diagnostic process, use a quality scanner to check for additional trouble codes. If any of these trouble codes are present, diagnose each one thoroughly before proceeding.

2 - Inspect PCM circuit wiring

Begin the diagnostic process with a thorough inspection of the vehicle's wiring harness in relation to the PCM itself. Check for broken/frayed wires or any wiring that may be corroded.

3 - Check the PCM connectors

Next, check each connector located along your vehicle's PCM housing. Make sure that all wires are securely fastened to their respective terminals and that there is no obvious damage associated with the contacts.

In addition, you should also check for signs of corrosion inside each connector. Any problems of this type should be corrected before proceeding.

4 - Check battery voltage

As simple as it sounds, it is also extremely important to check the vehicle's battery voltage when dealing with U0100 related issues. At rest, a fully charged battery should carry a charge of approximately 12,6 volts.

5 - Inspect the positive/grounded PCM power supply

Use the model specific wiring diagram to find the positive and ground sources for your vehicle's PCM. Using a digital multimeter, check for a positive signal and a ground signal with the vehicle ignition on.

6 - PCM Analysis

If steps #1 - #6 failed to identify the source of DTC U0100, there is a significant possibility that your vehicle's PCM has indeed failed. In this case, a replacement will be required.

Many PCMs also need to be "flashed" with the manufacturer's software to facilitate their proper use. This usually requires a trip to the local dealership.

How much does it cost to fix U0100?

U0100 Troubleshooting Cost , depends on the nature of the loss of communication and the brand of your car. It will take the mechanic about an hour to diagnose the cause of code U0100. If the problem is with your battery or the wiring between the CAN bus and the PCM, this might be a quick fix.  Replacing the ECM or the PCM itself can cost anywhere from 800 to 1500 dollars.