P0670 — Glow Plug Control Module Control Circuit/Open

Obd-II trouble code P0670 indicates a problem with the glow plug control module circuit. This code suggests an open or faulty circuit that affects the proper operation of the glow plug control system, which is crucial for starting diesel engines, especially in cold conditions. Note that the specific label or code may vary between different vehicle manufacturers, but the fundamental issue remains similar across makes and models.

System affected: Glow plug control circuit
Severity: Moderate to high, depending on symptoms
Main symptoms: Hard cold start, engine roughness, increased emissions
Driveability: Limited — vehicle may start but with difficulties

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Manufacturer variations for trouble code P0670

Different vehicle OEMs might label or interpret the P0670 code differently within their diagnostic systems. Such variations can sometimes cause confusion during diagnosis. Here are some known label variations associated with this trouble code:

Ford: P0670 — « Glow Plug Control Module Circuit/Open »
VW / Audi: Codes related to glow plug control circuit, sometimes labeled as « Glow Plug Controller Circuit – Open »
Mercedes-Benz: Similar control circuit fault codes, often within the P06xx range, with specific references to glow plug control
Peugeot / Citroën: Corresponding fault labels indicating glow plug circuit issues

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What does trouble code P0670 mean?

In simple terms, P0670 indicates that the vehicle’s onboard computer, known as the Engine Control Unit (ECU), has detected an electrical problem within the glow plug control module circuit. The ECU monitors this circuit to ensure proper activation of the glow plugs, which are essential components that heat the air in the combustion chamber of diesel engines to facilitate starting, especially in cold weather.

This code is triggered when the ECU detects an open circuit, short circuit, or malfunction within the glow plug control circuit. Commonly, this problem arises if there’s a wiring issue, a faulty control module, or a problematic glow plug relay. Typically, the issue appears after repeated failed attempts to start the engine or during cold weather when the glow plugs are most needed.

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Severity and risks of trouble code P0670

The severity of P0670 largely depends on the driving conditions and the root cause. If the glow plug control circuit is open or malfunctioning, it can lead to difficulties in starting the engine, especially in low temperatures. As a result, the vehicle may experience extended cranking times or fail to start altogether. Additionally, a faulty glow plug control system can increase emissions due to incomplete combustion and potentially cause engine roughness during warm-up.

In terms of risks, persistent starting issues can cause stranded vehicle situations, and continuous driving with compromised glow plug functionality mayS contribute to further damage or higher repair costs over time. However, the vehicle can generally be driven if started without too much trouble, but it’s advisable to diagnose and repair the problem promptly to avoid worsening conditions.

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Symptoms of trouble code P0670

Common symptoms associated with P0670 reflect the underlying glow plug system issues. Drivers often notice that the vehicle struggles to start in cold weather, or the engine may run rough initially. Other signs include increased exhaust emissions, the illumination of warning lights, and possibly odd engine behaviour during warm-up phases.

Difficulty starting the engine, particularly in cold conditions
Engine roughness or misfire during warm-up
Excessive cranking time before the engine starts
Illumination of the Check Engine Light
Potential increase in exhaust smoke during cold starts

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Most likely causes of trouble code P0670

This code typically stems from issues within the glow plug control circuit. Understanding the common causes helps narrow down the diagnostic process. The causes below are ranked from the most frequent to the less common:

Faulty glow plug control module: If the control module itself is malfunctioning or has internal faults, it can trigger this code by failing to complete circuit monitoring.
Wiring or connector problems: Corrosion, damaged wires, or loose connections in the glow plug circuit are frequent culprits, causing open circuits or faulty signals.
Blown fuse or relay: An electrical component such as a fuse or relay dedicated to glow plug operation can fail, cutting off power or control signals.
Faulty glow plugs: While less common for this specific code, defective glow plugs or their wiring may contribute to false signals or circuit issues.
ECU software or sensor failure: Rare but possible, where a glitch in the ECU or surrounding sensors might falsely trigger this code without actual hardware issues.

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How to diagnose trouble code P0670

The diagnostic process for P0670 involves systematic checks to identify the root cause safely and efficiently. Here are the steps, keeping in mind that some procedures require specific tools or expertise:

Visual Inspection: Examine the wiring harness connected to the glow plug control module. Look for signs of damage, corrosion, or loose connections.
Check fuse and relay: Verify the relevant fuse and relay for the glow plug circuit are intact and functioning properly, replacing them if necessary.
Scan live data: Using a professional-grade scan tool, observe the signals from the glow plug control module and related sensors to check circuit status during vehicle startup.
Testing wiring continuity: Employ a multimeter to check for continuity in wiring between the control module, glow plugs, and power sources. Look for open circuits.
Test the control module: If accessible, test the glow plug control module for proper operation, or swap it temporarily with a known good unit if available.
Check glow plugs: Test individual glow plugs for resistance and proper operation, replacing any that show faults.

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Possible repairs for trouble code P0670

Restoring proper function involves addressing the root causes identified during diagnosis. The repairs can vary from simple to complex, often requiring professional skills, especially for electrical components.

Replace faulty glow plug control module: Often a professional repair due to integration with the vehicle’s electrical system.
Repair or replace wiring and connectors: Correcting damaged wires or securing loose connections is a basic repair that can often be performed by a skilled DIYer.
Replace blown fuse or relay: A straightforward fix that typically involves locating and replacing the component following the vehicle’s fuse diagram.
Replace defective glow plugs: Involves removing and installing new glow plugs, which may require engine cooling and proper tools.
Update ECU software: In rare cases, flashing or reprogramming the ECU might be necessary if the fault is related to software glitches.

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Vehicles commonly associated with trouble code P0670 in Europe

While P0670 is not specific to a particular brand, certain models and engine families frequently report glow plug circuit issues. In Europe, diesel vehicles are more susceptible due to the operational demands of the glow plug system. Here are some known associations:

Volkswagen Group: Common in various TDI engines (e.g., 2.0 TDI, 1.9 TDI)

Ford: Various diesel models, especially certain Transit and Fiesta models with diesel engines

Peugeot / Citroën: Common in HDI diesel engines across multiple vehicle ranges

Mercedes-Benz: Many diesel engines, especially common rail systems

Renault: Particularly in dCi diesel engines

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Frequent mistakes with trouble code P0670

Diagnosing and repairing glow plug circuits requires care. A few common mistakes can lead to ineffective repairs or further complications:

Assuming the glow plugs are always the cause: Often, wiring or control module faults are the root issue, not the glow plugs themselves.
Neglecting to check electrical wiring: Overlooking wiring integrity can result in persistent faults even after replacing modules or glow plugs.
Replacing parts without proper testing: Replacing components blindly without testing can waste time and money.
Failing to follow manufacturer procedures: For complex systems, procedural steps specific to the OEM should be adhered to for accurate diagnosis and repair.

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FAQ — trouble code P0670

Can this code disappear on its own? No, P0670 usually requires a correction to the underlying electrical issue. Clearing the code without fixing the problem will often lead to it returning.

Can I keep driving? If the vehicle starts and runs normally at ambient temperatures, driving is possible but not recommended until diagnosed. Persistent starting issues or engine misfire on cold starts suggest you should seek repairs promptly.

Why does the code return after clearing? Because the underlying circuit or component fault persists. The ECU continually monitors the glow plug circuit, so unless the root cause is resolved, the code will reappear.