P06F9

What it means

P06F9 means the control unit has detected a problem with the supply voltage to glow plug control module 2, the second glow plug module on engines that use more than one. The voltage was outside the expected range, or did not agree with other voltage readings, long enough to set the fault. The exact thresholds and module layout depend on the vehicle and engine.

Symptoms

• Engine management or glow plug warning light on
• Hard or slow starting when cold, especially in cold weather
• White smoke or rough running for the first moments after a cold start
• Glow plugs on one bank or cylinder group not heating
• Other low voltage or charging system codes stored alongside it

Possible causes

• Weak, discharged or ageing battery causing low system voltage during glow plug operationlikely
• Corroded, loose or damaged power or earth connections at the battery, module or engine earth pointslikely
• Faulty or blown fuse, relay or supply wiring feeding glow plug control module 2possible
• Charging system fault (alternator or regulator) giving low or excessive voltagepossible
• Damaged wiring or connector at the module, such as chafing, water ingress or pin damagepossible
• Internal fault in glow plug control module 2 causing incorrect voltage monitoringrare
• Outdated control unit software where the manufacturer has documented it as a known causerare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting battery voltage, engine temperature and whether other voltage or glow plug codes are present.
2. Visually inspect the battery terminals, main power and earth cables, fuses and the glow plug module 2 wiring and connectors for corrosion, damage or water ingress.
3. Test the battery state of health and measure resting voltage, then voltage while cranking.
4. Test the charging system output with the engine running and with loads switched on, against the manufacturer's specification.
5. Check the relevant fuses and relays for the glow plug system, using the wiring diagram for the specific model and engine.
6. Using the wiring diagram, check the supply and earth at the module 2 connector and perform voltage drop tests on the power and earth circuits under load.
7. Check the module and glow plug circuit operation with a live data or actuator test if the vehicle supports it.
8. Check for manufacturer service bulletins or software updates relating to this code on the specific vehicle.

How to fix

• Recharge or replace the battery if it fails testing.
• Clean and tighten, or repair, the battery, power and earth connections.
• Replace any faulty fuse or relay, after finding out why it failed.
• Repair or replace damaged wiring or connectors in the glow plug module 2 supply and earth circuits.
• Repair or replace the alternator or regulator if the charging voltage is out of specification.
• Replace glow plug control module 2 only once the supply and earth circuits are proven good, and update the software if the manufacturer lists it as a known fix.

Can I keep driving?

Nearby codes

• P06F8GenericGlow Plug Control Module 2 Control Circuit High
• P06FAGenericGlow Plug Control Module 2 Performance