U0101 Lost Communication With Transmission Control Module (TCM)

Code U0101 - means Lost Communication with TCM.

The transmission control module (TCM) is the computer that controls your vehicle's transmission. Various sensors provide input to the TCM. It then uses this information to determine the control of various outputs such as the shift solenoids and the torque converter clutch solenoid.

There are a number of other computers (called modules) on board the vehicle. The TCM communicates with these modules via the Controller Area Network (CAN) bus. CAN is a two-wire bus consisting of CAN High and CAN Low lines. There are two terminating resistors, one at each end of the CAN bus. They are required to terminate communication signals that travel in both directions.

Code U0101 indicates that the TCM is not receiving or transmitting messages on the CAN bus.

OBD-II Trouble Code - U0101 - Data Sheet

U0101 - means that the communication with the transmission control module (TCM) is broken

What does code U0101 mean?

This is a generic communications DTC that applies to most makes and models of vehicles, including but not limited to Chevrolet, Cadillac, Ford, GMC, Mazda, and Nissan. This code means the transmission control module (TCM) 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. Without this CAN bus, control modules cannot communicate and your scan tool may not receive information from the vehicle, depending on which circuit is involved.

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.

Modules connected to the high-speed serial data control circuit of the General Motor Local Area Network (GMLAN) to transmit serial data during normal vehicle operation. Operational information and commands are exchanged between modules. The modules have pre-recorded information about what messages should be exchanged over the serial data circuits for each virtual network. Messages are monitored and, in addition, some periodic messages are used by the receiver module as an indication of the availability of the transmitter module. The control latency is 250 ms. Each message contains the identification number of the transmitter module.

Symptoms of code U0101

Symptoms of a U0101 engine code may include:

• Malfunction Indicator Lamp (MIL) illuminated
• Vehicle does not shift gears
• The car remains in one gear (usually 2nd or 3rd).
• Codes P0700 and U0100 will most likely appear along with U0101.
  

Causes of Fault U0101

Usually the reason for installing this code is:

• Open in CAN + bus circuit
• Open in the CAN bus - electrical circuit
• Short circuit to power in any CAN bus circuit
• Short to ground in any CAN bus circuit
• Rarely - the control module is faulty
• Low battery

How To Fix Code U0101 | TCM Not Communication With ECU Troubleshooting | Gear Shifting Problem

Diagnostic and repair procedures

A good starting point is always to check the Technical Service Bulletins (TSB) for your particular vehicle. Your problem may be a known issue with a known manufacturer-released fix and could save you time and money while troubleshooting.

First, look for other DTCs. If any of these are bus communication or battery / ignition related, diagnose them first. Misdiagnosis is known to occur if you diagnose the U0101 code before any of the major codes are thoroughly diagnosed and rejected.

If your scan tool can access trouble codes and the only code you are getting from other modules is U0101, try talking to the TCM. If you can access the codes from the TCM, then code U0101 is either an intermittent or memory code. If you can't talk to the TCM, then code U0101 that other modules are setting is active and the problem already exists.

The most common failure is a loss of power or ground.

Check all fuses supplying the TCM on this vehicle. Check all TCM ground connections. 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 DTCs from all modules that set the code in memory and see if U0101 returns or you can talk to the TCM. If no code is returned or communication with the TCM is restored, the problem is most likely a fuse / connection issue.

If the code returns, look for the CAN bus connections on your specific vehicle, especially the TCM connector located behind the dashboard. Disconnect the negative battery cable before disconnecting the connector on the TCM. 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 dielectric silicone grease where the terminals touch.

Perform these few voltage checks before plugging the connectors back into the TCM. You will need access to a digital volt ohmmeter (DVOM). Make sure the TCM has power and ground. Access the wiring diagram and determine where the primary power and ground supplies go into the TCM. Connect the battery before proceeding with the TCM disconnected. Connect the red wire from the voltmeter to each B + (battery voltage) power source going to the TCM connector and the black wire from the voltmeter to a good ground (if unsure, the negative pole of the battery is always working). You should see the battery voltage reading. Make sure you have a good reason. Connect the red wire from the voltmeter to battery positive (B +) and the black wire to each ground. Once again, you should see the battery voltage every time you plug it in. If not, troubleshoot 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.

If all tests pass and communication is still not possible, or you were unable to reset DTC U0101, the only thing to do is to seek help from a trained automotive diagnostician, as this will indicate a faulty TCM. Most of these TCMs need to be programmed or calibrated for the vehicle in order to install them correctly.

U0101 - causes

How to diagnose U0101

To diagnose DTC U0101, a technician must:

1. Check the manufacturer's TSB to see if there is a known cause or remedy.
2. If nothing is found, check the CAN bus system wiring and connections for signs of wear and corrosion.
3. Any grounds, fuses or relays that are connected to the TCM should also be investigated.
4. If no problems are found at this stage, the TCM needs to be checked.

Diagnostic errors 

The following are common errors when diagnosing DTC U0101:

1. Mistaking engine noise as a sign of a problem with the TCM
2. Not checking for corrosion on battery terminals
3. Not investigating if any fuses are blown or relays are faulty
4. Ignoring signs of car wiring wear

How serious is the code U0101

Code U0101 is serious, but it doesn't mean you should get rid of the car. The TCM is not an essential system in your vehicle. It controls one part of the transmission, the torque converter clutch solenoid circuit. Also, U0101 could be the result of a minor issue with your transmission system, or even an overheating issue.

What repairs might be required for U0101?

Below are solutions that can fix this problem:

1. Replacement of TSM
2. Replacing damaged or worn wiring
3. Reset the PCM or TCM by disconnecting battery power for 10 minutes.
4. Check for corrosion on battery terminals and connections to clean them.

Code U0101 is a bit more difficult to diagnose as there is no unique solution that solves it. Most people just leave repairs to their auto mechanics. You can try to fix it yourself, but you will need the help of online instructions or repair guides.

Related codes

Code U0101 is associated with and may be accompanied by the following codes:

• U0100 - Loss of K-line
• U0102 - Transmission Output Speed ​​Sensor (POS) Circuit High Input 
• U0103 - Intermittent signal in the transmission speed sensor circuit (POS) 
• U0104 Transmission Fluid Temperature (TFT) Sensor Circuit Range/Performance 
• U0106 - Open circuit in the torque converter clutch solenoid valve circuit 
• U0201 No message from ECM/PCM to TCM or codes U0100 and U0102 are present

How much does it cost to fix code U0101?

The cost of repairing code U0101 depends on the severity of the problem that caused it. If you bought your car recently, the U0101 code may be a minor issue that does not require a major fix. You can fix it within an hour or two. In most cases, you just need to replace the TCM.

If the problem is more serious, you may have to wait a little longer because the part will need to be ordered first. The cost of a TCM replacement can range from $400 to $1500. Typically, you won't pay more than $1000 for this type of repair. If you don't want to spend that much money on repairs all at once, then just find someone who specializes in car repairs and see if they can fix it for less or let you pay in installments instead of shelling out all the money. immediately.

U0101 Brand specific information

• U0101 BUICK Lost Communication With Transmission Control Module
• U0101 CADILLAC Lost Communication With Transmission Control Module
• U0101 CHEVROLET Lost Communication With Transmission Control Module
• CHRYSLER transmission bus message U0101
• U0101 DODGE transmission bus message
• U0101 FORD Lost Communication with Transmission Control Module
• U0101 GMC has lost communication with the transmission control module
• U0101 HUMMER Lost communication with transmission control module
• U0101 INFINITI Lost Communication with Transmission Control Module
• U0101 JEEP transmission bus message
• U0101 LEXUS Lost Communication With Transmission Control Module
• U0101 LINCOLN Lost Communication With Transmission Control Module
• U0101 MAZDA Lost Communication with Transmission Control Module
• U0101 MERCURY Lost Communication With Transmission Control Module
• U0101 NISSAN Lost Communication With Transmission Control Module
• U0101 PONTIAC Lost Communication with Transmission Control Module
• U0101 SATURN Lost Communication With Transmission Control Module
• U0101 SCION lost communication with transmission control module
• U0101 TOYOTA Lost Communication With Transmission Control Module

Conclusion:

U0101 is often misdiagnosed as a TCM malfunction prior to checking the wiring harness.

DTC U0101 rarely appears on its own. Use other codes as clues to help you narrow down possible causes.