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Engine-Codes – Generic – U1842

U1842 Code - Lost Communication With ECM/PCM

Quick Answer

The U1842 diagnostic trouble code (DTC) indicates that there is a communication failure between the electronic control module (ECM) or powertrain control module (PCM) and other control modules within the vehicle. Common causes include Loose or damaged wiring/connectors between the ECM/PCM and other modules, Faulty ECM/PCM, Corrosion or water damage to the ECM/PCM. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
U1842 indicates Lost Communication With ECM/PCM.
Common causes
Common causes include Loose or damaged wiring/connectors between the ECM/PCM and other modules, Faulty ECM/PCM, Corrosion or water damage to the ECM/PCM.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 09, 2024
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Code U1842 Description

The U1842 diagnostic trouble code (DTC) indicates that there is a communication failure between the electronic control module (ECM) or powertrain control module (PCM) and other control modules within the vehicle. The ECM/PCM plays a crucial role in managing various engine functions, such as fuel injection, ignition timing, and emissions control. When communication with the ECM/PCM is lost, it can lead to significant performance issues and potentially cause the vehicle to stall or not start at all.

OBDII Code U1842 - Lost Communication With ECM/PCM
U1842 Code - Lost Communication With ECM/PCM

Common Causes of U1842

  1. Loose or damaged wiring/connectors between the ECM/PCM and other modules.
  2. Faulty ECM/PCM.
  3. Corrosion or water damage to the ECM/PCM.
  4. Software issues or glitches in the ECM/PCM.
  5. Electrical interference from aftermarket accessories or modifications.

Symptoms of U1842

  1. Check Engine Light (CEL) illuminated on the dashboard.
  2. Engine may stall or have difficulty starting.
  3. Erratic engine performance, such as rough idling or hesitation.
  4. Loss of power or reduced acceleration.
  5. Transmission shifting irregularities.

How to Fix U1842

  1. Begin by conducting a thorough visual inspection of the wiring harness and connectors, looking for any signs of damage, corrosion, or loose connections.
  2. Test the ECM/PCM using a diagnostic scan tool to check for any internal faults or software issues. If necessary, reprogram or replace the ECM/PCM.
  3. Clear the DTC and reset the ECM/PCM to see if the communication issue persists.
  4. Check for any aftermarket accessories or modifications that could be causing interference with the ECM/PCM, and remove or relocate them if needed.
  5. If the issue persists, consult with a professional mechanic or dealership for further diagnosis and repair.

Cost to Fix U1842

The cost of repairing a U1842 code can vary depending on the specific cause of the communication failure. In general, replacing a faulty ECM/PCM can range from $500 to $1500, including parts and labor. However, the total repair cost may increase if additional components or wiring repairs are needed. It is important to factor in diagnostic time and labor rates, which can vary based on location and the complexity of the repair. It is recommended to obtain quotes from multiple repair shops to compare costs and ensure a fair price for the repair.

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Code U1842 Information for Specific Makes

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about U1842 Code

1. What does the OBDII code U1842 mean?

U1842 indicates a loss of communication between the vehicle's Engine Control Module (ECM) or Powertrain Control Module (PCM) and another control module on the communication network.

2. What are the common symptoms of code U1842?

Symptoms may include the check engine light or other warning lights illuminating, poor engine performance, reduced fuel efficiency, or the vehicle entering limp mode.

3. What causes the U1842 code to appear?

The code can be caused by issues such as a faulty ECM/PCM, damaged communication wiring, corroded or loose connectors, or a failure in another module on the network.

4. Can a weak battery cause the U1842 code?

Yes, a weak or failing battery can disrupt the communication network and trigger the U1842 code.

5. How is the U1842 code diagnosed?

A technician will use a scan tool to check for related codes, inspect wiring and connectors, and test the communication network to identify the source of the issue.

6. Can I drive with the U1842 code active?

Driving with this code is not recommended as it may cause poor engine performance or trigger limp mode, potentially leading to unsafe driving conditions.

7. What tools are needed to troubleshoot the U1842 code?

Common tools include an OBDII scanner, a multimeter for testing electrical circuits, and wiring diagrams specific to your vehicle.

8. Is the U1842 code specific to certain vehicle brands?

While U1842 is a generic communication code, its exact meaning and troubleshooting steps may vary depending on the vehicle's make and model.

9. What repairs might fix the U1842 code?

Repairs can include replacing damaged wiring, cleaning or securing connectors, reprogramming or replacing the ECM/PCM, or addressing faults in other modules.

10. How much does it cost to fix the U1842 code?

Repair costs can vary widely, ranging from $50 to $300 for minor wiring repairs, or $500 to $1,500 if a module replacement is required.

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