OBD-II trouble code
P0670: Glow Plug Control Module Circuit
The engine control module detected a fault in the glow plug control module circuit on a diesel engine. The module that powers the glow plugs isn't responding correctly, which can cause hard cold starts and rough cold running.
Quick facts
- System
- Powertrain
- Category
- Auxiliary Emissions Controls
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $700
- DIY difficulty
- Intermediate DIY
Browse every code in P0600–P06DD, or start from the full code library.
What does P0670 mean?
Diesel engines use glow plugs to pre-heat the combustion chambers so the engine will start and run smoothly when cold. A glow plug control module manages when and how long the glow plugs are energized, and it reports its status back to the engine control module (ECM). P0670 sets when the ECM detects a fault in the glow plug control module circuit — the module isn't responding as expected, or the ECM can't confirm it is operating correctly. This is a module/circuit-level code (the control side), distinct from a code that names a specific cylinder's glow plug.
Because glow plugs mainly matter for cold starting, symptoms are most noticeable in cold weather: hard starting, extended cranking, rough running or white smoke until the engine warms, and often the glow-plug (wait-to-start) indicator behaving oddly. Common causes are a failed glow plug control module, wiring or connector faults between the module and the ECM or plugs, a blown fuse or poor ground, and sometimes failed glow plugs loading the circuit. Diagnosis verifies the module's power, ground, and control wiring and checks the glow plugs before deciding whether the module itself needs replacement.
Common causes
- Blown fuse or poor ground feeding the glow-plug circuit
- Damaged, corroded, or loose wiring/connectors at the module
- Water intrusion or corrosion at the module location
- One or more failed glow plugs loading the circuit
- Failed glow plug control module, which is the usual endpoint once the fuse, the wiring and the plugs have been cleared
- Module replaced without correct programming on some vehicles
Symptoms
- Hard cold starting or extended cranking
- Rough running or white smoke until warm
- Glow-plug / wait-to-start indicator on or behaving abnormally
- Check engine light with P0670 stored
- Reduced cold-weather driveability
Diagnostic steps
- 1.Scan and record all codes; note any cylinder-specific glow-plug codes (such as P0671).
- 2.Check the glow-plug fuse and the module's power and ground feeds.
- 3.Inspect the control module connectors and wiring for corrosion, damage, and water intrusion.
- 4.Test the glow plugs for resistance with the ignition off, the key out and the engine cool — each plug draws tens of amps while glowing and the plugs themselves sit in the cylinder head at engine temperature. Disconnect each plug's lead individually, removing the bus bar or strap where one is fitted, so the plugs are not measured in parallel. A healthy plug reads from a fraction of an ohm up to a few ohms, which is the same order as the meter's own test leads, so touch the leads together and subtract that offset before judging anything or the test will condemn good plugs. An infinite reading is a failed plug.
- 5.Verify the module's control signal from the ECM where service data is available.
- 6.If wiring, fuse, ground, and plugs are good but the circuit is still faulted, replace the glow plug control module.
Repair cost
$100 – $700
A glow plug control module replacement commonly runs $150-$500 with labor; replacing glow plugs adds cost and varies with access. Wiring or fuse repairs are cheaper. Confirm whether the fault is the module, the wiring, or the plugs before buying parts.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with glow plug / glow plug module replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.