U0688: Lost Communication With Throttle Position Sensor/Switch G

What it means

The vehicle bus reports loss of communication with smart throttle position sensor G. The ECM loses one of the redundant throttle channels and reverts to a fail-safe map.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

Throttle position sensor channel G is a networked input used with other throttle channels to monitor electronic throttle operation. This code sets when messages from channel G are lost, prompting the engine controller to discard that input and use a fail-safe throttle strategy.

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. Save freeze-frame data and scan all modules for throttle and communication codes to check whether channel G loss coincides with a wider network issue.
2. Check live data for channel G's status and reading alongside the other throttle channels while operating the throttle only as the manufacturer's procedure allows.
3. Inspect channel G's connector and bus wiring for loose pins, corrosion, water intrusion, chafing, or heat damage near the throttle body.
4. Verify the sensor or module power and ground according to the manufacturer's procedure.
5. Test channel G's bus branch for opens or shorts, then assess the sensor or module if wiring and supplies are correct.

Common fixes

• Reconnect or clean the channel G connector.
• Repair damaged channel G bus wiring or terminals.
• Restore a faulty power or ground connection to the sensor or module.
• Replace the channel G sensor or module if circuit checks confirm an internal failure.

Can I keep driving?

Throttle control may be limited or unpredictable, so avoid driving in traffic or at speed and stop if the vehicle does not respond consistently. The controller may restrict engine power to protect against an unreliable throttle signal.