U0673: Lost Communication With Ion Sense Module

What it means

The vehicle bus reports loss of communication with the ion sense module (used for misfire/knock detection via ionisation current at the spark plug). Per-cylinder feedback is unavailable; misfire monitor falls back to crankshaft-deceleration logic only.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test

How it works

The ion sense module uses electrical signals at the spark plugs to help detect combustion knock and identify misfires by cylinder. The control module sets U0673 when it loses network communication with that module, removing cylinder-specific feedback and leaving the misfire monitor to rely on crankshaft speed changes.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

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. Scan all modules for communication and misfire codes, and review freeze-frame data for engine load and whether the ion sense module dropped out with other devices.
2. Check scan-tool data to confirm whether the ion sense module is online and whether per-cylinder misfire or ion-sensing data is unavailable.
3. Inspect the module connector and harness near the ignition system for looseness, corrosion, heat damage, or chafing.
4. Using the manufacturer's wiring information, verify module power and ground and test its network wiring for opens, shorts, or poor connections.
5. If wiring and supplies are sound, test network communication at the ion sense module and determine whether the module has failed.

Common fixes

• Reconnect or clean the ion sense module connector and repair damaged wiring.
• Restore a missing or poor power or ground connection to the module.
• Repair an open or short in the vehicle network wiring to the ion sense module.
• Replace the ion sense module if its power, ground, and network connections are good but it remains offline.

Can I keep driving?

If the engine runs smoothly, a short gentle trip may be possible, but avoid heavy loads because knock and cylinder-specific misfire detection are reduced. Stop driving if the engine misfires, loses power, or the check-engine light flashes, as continued misfire can damage the catalytic converter.