U0115: Lost Communication with ECM/PCM B

What it means

A control module has lost communication with ECM/PCM B. The code does not establish why communication was lost or whether the engine can run; those effects depend on the vehicle and reporting module.

How it works

ECM/PCM B is a separately designated engine or powertrain control module on vehicles that use more than one. Other modules expect messages from this specific module; U0115 sets when communication with module B is lost. It does not establish that ECM/PCM A has failed, why module B is offline, or whether the engine will continue to run.

Common causes

Most likely first.

1. Loss of ECM/PCM power or ground
2. Open, shorted, or damaged communication wiring or connector
3. ECM/PCM or gateway fault

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Save the all-module scan and freeze-frame data, distinguishing reports naming ECM/PCM B from any that name ECM/PCM A.
2. Check battery condition and the fuses, power, and ground connections assigned to ECM/PCM B.
3. Inspect module B's connectors and communication wiring for corrosion, loose pins, water entry, or harness damage.
4. Use a scan tool to check whether ECM/PCM B responds and whether other modules on the same network are also offline.
5. If its power and ground are correct but it does not respond, test the network circuit and gateway route for module B to the manufacturer's specification.

Common fixes

• Charge or replace a weak battery and repair poor battery connections.
• Replace a failed fuse or repair ECM/PCM B's power or ground connection.
• Repair damaged network wiring or clean and secure the connector at ECM/PCM B.
• Repair a confirmed gateway fault that prevents communication with module B.
• Replace or reprogram ECM/PCM B only after its supply and network circuits pass testing.

Can I keep driving?

If the engine runs normally and no warning indicates loss of powertrain control, drive only as needed and monitor for changes; the effects depend on the vehicle and reporting module. Stop if the engine stalls, power becomes unpredictable, or a serious warning appears.