AutoCodes – Generic – U1842

U1842 Code - Lost Communication With ECM/PCM

Quick Answer

The system voltage is between 9-16 volts. Common causes include Faulty Engine Control Module (ECM)/Powertrain Control Module (PCM), Engine Control Module /Powertrain Control Module harness is open or shorted, Engine Control Module /Powertrain Control Module circuit poor electrical connection. 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 Faulty Engine Control Module (ECM)/Powertrain Control Module (PCM), Engine Control Module /Powertrain Control Module harness is open or shorted, Engine Control Module /Powertrain Control Module circuit poor electrical connection.
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.

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Code Popularity 1,461

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jun 08, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U1842 Description

The system voltage is between 9-16 volts. The vehicle power mode master indicates that the need for serial data communications. The Diagnostic Trouble Code (DTC) will set when a supervised periodic message that includes the transmitter device availability has not been received.

OBDII Code U1842 - Lost Communication With ECM/PCM - AutoCodes.com — U1842 Code - Lost Communication With ECM/PCM

What does this mean?

What are the Possible Causes of the DTC U1842?

Faulty Engine Control Module (ECM)/Powertrain Control Module (PCM)
Engine Control Module /Powertrain Control Module harness is open or shorted
Engine Control Module /Powertrain Control Module circuit poor electrical connection

How to Fix the DTC U1842?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the U1842 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the U1842 code?

Need more information on how to fix the U1842 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U1842 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

U1842 Buick — Lost Communication With ECM/PCM
U1842 Cadillac — Lost Communication With ECM/PCM
U1842 Chevrolet — Lost Communication With ECM/PCM
U1842 GMC — Lost Communication With ECM/PCM

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.