P0668

What it means

P0668 is a generic code meaning the engine or powertrain control module has detected a low signal from its internal temperature sensor (circuit A). The module monitors its own internal temperature, and the voltage it saw was below the expected range, suggesting a short to ground or a fault inside the module itself.

Symptoms

• Engine management warning light on
• Usually no noticeable change in driving
• Possible reduced performance or limp mode if the module applies protective strategies
• Other stored fault codes, especially module or sensor supply faults
• Intermittent starting or stalling in rare cases

Possible causes

• Internal fault in the control module (temperature sensing circuit or its electronics)likely
• Low or unstable supply voltage to the module caused by a weak battery or charging faultpossible
• Poor or corroded module power or earth connectionspossible
• Water ingress, corrosion or heat damage inside the module or at its connectorspossible
• Damaged wiring or connector pins at the module causing a short to earthrare
• Outdated or faulty module software where the manufacturer has issued a correctionrare

How to diagnose

1. Read all stored codes and freeze frame data, noting battery voltage, engine temperature and conditions when the code set
2. Check whether other module, voltage or communication codes are present and deal with those first
3. Test battery condition and charging system output to confirm stable supply voltage
4. Inspect the module, its connectors and surrounding area for water, corrosion, heat damage or physical damage
5. Check the module power feeds and earth connections for voltage drop under load, following the model wiring diagram
6. Clear the code and road test to see whether it returns immediately or only under certain conditions
7. Check for manufacturer software updates or technical bulletins relevant to the model and engine
8. If the fault persists with sound supply and wiring, have the module tested or replaced and programmed as the manufacturer specifies

How to fix

• Repair or replace corroded or loose power and earth connections
• Replace a weak battery or repair the charging system fault
• Repair damaged wiring or connector terminals and dry out or seal any water ingress
• Update the module software where a correction is available for the vehicle
• Replace and correctly program the control module if an internal fault is confirmed

Can I keep driving?

Nearby codes

• P0667GenericControl Module Internal Temperature Sensor A Range/Performance
• P0669GenericControl Module Internal Temperature Sensor A Circuit High