P0670 is a generic OBD-II powertrain code standardized as “Glow Plug Control Module Control Circuit.” It applies to diesel engines equipped with a dedicated glow plug control module.
This code indicates the powertrain control module detected an electrical fault in the control circuit. It does not automatically prove the module itself has failed.
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Key Takeaways
- P0670 indicates an electrical fault detected in the glow plug control module circuit of a diesel engine.
- Possible causes include damaged wiring, corroded connectors, or a failed glow plug control module.
- Diagnosis requires testing the control circuit for continuity, voltage, and proper ground signals.
- Repairs depend on confirmed electrical or component faults, not trial-and-error part replacement.
P0670 Code Description and Implications
P0670 is a generic OBD-II powertrain code standardized by SAE as “Glow Plug Control Module Control Circuit.”
It applies to diesel engines that use a dedicated glow plug control module to manage the heating cycles for cold starting and emissions control.
The powertrain control module (PCM) monitors the electrical signals and control circuits communicating with the glow plug control module.
When the PCM detects an open circuit, a short to ground, or an abnormal voltage signal in this specific control path, it stores P0670.
This code identifies a detected electrical fault condition in the module control circuit; it does not automatically prove that the glow plug control module itself has failed internally.
Common Causes of the P0670 Code
Because P0670 specifically identifies an electrical circuit fault for the control module, the root cause usually involves an interruption or abnormal resistance in that path.
Possible causes include damaged, broken, or severely corroded wiring in the harness connecting the PCM to the glow plug control module.
A loose, disconnected, or corroded electrical connector at the module or the PCM can also interrupt the circuit.
A failed internal driver or open circuit within the glow plug control module itself may trigger this code.
In rare cases, a failed PCM or internal control module fault may prevent proper communication with the glow plug system.
Symptoms Associated With P0670
The most consistent symptom is an illuminated Check Engine Light or a flashing glow plug indicator light on the dashboard.
Because the glow plug control module manages the heating cycles, a fault may prevent the glow plugs from activating during cold starts.
This can lead to extended cranking times, difficulty starting in cold weather, or white smoke from the exhaust due to incomplete combustion.
Some applications may exhibit rough idling or misfires until the engine reaches operating temperature.
MIL behavior varies by application. Some vehicles may illuminate the Check Engine Light immediately, while others may store the DTC without commanding it.
Diagnosing the P0670 Trouble Code
Diagnosis must begin by confirming the exact factory definition and technical service bulletins for the specific make, model, and engine.
Retrieve the code and record any freeze-frame data or related OBD2 codes using a scan tool.
Visually inspect the wiring harness and electrical connectors at the glow plug control module and the PCM for physical damage, chafing, or corrosion.
Check the control circuit for continuity and verify the presence of proper reference voltage and ground signals according to the manufacturer wiring diagram.
If the wiring and connectors test within specifications, further diagnosis of the glow plug control module or PCM driver circuit may be required.
Repairing the P0670 Issue
Repairs must follow the confirmed root cause identified during electrical testing.
If wiring damage or a broken trace is found, repair or replace the affected harness section and clear the code.
If the electrical connector is corroded or damaged, repair the terminals or replace the connector pigtail.
If the glow plug control module fails the manufacturer’s electrical and functional tests, replace the module with a component meeting the correct vehicle specification.
If the PCM is confirmed as the source of the open circuit, follow the applicable module replacement and programming procedure.
Always clear the codes and perform a cold-start test to verify the repair and ensure the monitor completes successfully.
Cost Considerations for P0670 Repairs
Repair costs for P0670 vary based on the underlying fault, vehicle accessibility, and local labor rates.
Wiring repairs or connector replacements are typically the least expensive fixes, requiring only minor labor and basic materials.
Replacing a dedicated glow plug control module involves moderate parts costs, though labor time increases if the module is mounted in a difficult-to-access location.
If the repair requires replacing and programming the PCM, parts and diagnostic costs will be higher.
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Prevention Strategies for Future Occurrences
Keeping electrical connectors clean and ensuring wiring harnesses near hot exhaust components or moving parts are securely routed can help prevent heat-related damage or chafing.
Inspecting exposed wiring during routine service can help identify developing damage or moisture intrusion before it causes an open circuit.
Using dielectric grease on electrical connections where specified by the manufacturer may reduce corrosion in harsh environments.
Troubleshooting Tips and Best Practices
Do not assume a P0670 code automatically requires replacing the glow plug control module; an open wire or a bad ground will produce the exact same electrical signature.
If multiple glow plug circuit codes are present alongside P0670, inspect the main power supply, shared grounds, or the primary module connector before testing individual circuits.
Check for applicable technical service bulletins or software updates, as some manufacturers release PCM recalibrations or updated module part numbers to address premature circuit failures.
Verify that aftermarket accessories or remote start systems are not interfering with the factory glow plug control wiring.
More OBD-II Codes
| P0657 | P0654 | P0652 | P0651 |
| P0650 | P0645 | P0672 | P0673 |
| P0674 | P0675 | P0676 | P0677 |
| P0683 | P0685 | P0688 | P0690 |
| P0691 | P0700 | P0600 | P0601 |
| P0602 | P0603 | P0604 | P0605 |
Frequently Asked Questions
Is P0670 a generic or manufacturer-specific code?
Yes. P0670 is a generic OBD-II code standardized by SAE. It carries the same basic definition across all diesel manufacturers, though exact diagnostic procedures vary by vehicle application.
Can a bad glow plug cause a P0670 code?
No. P0670 specifically identifies a fault in the glow plug control module circuit, not the individual glow plugs. However, a shorted glow plug could theoretically affect the module, so testing is required.
Will P0670 clear itself if the weather gets warmer?
Not automatically. If an open circuit or failed module triggered the code, the physical fault remains. The monitor may pass during warm weather, but the stored code requires a scan tool to clear.
Is it safe to drive with the P0670 code active?
The vehicle is usually safe to drive to a repair facility, especially in warm weather. However, in freezing temperatures, the engine may be difficult to start or may run roughly until it warms up.
Does P0670 mean I need to replace the PCM?
No. While a failed PCM can cause this code, wiring damage, corroded connectors, or a failed glow plug control module are also possible causes. Never replace the PCM without confirming the exact factory diagnostic procedure.
What Should You Do About the P0670 Code?
Confirm the exact factory definition and technical service bulletins for your specific diesel engine application.
Follow the applicable manufacturer diagnostic procedure to test the glow plug control module wiring harness, connectors, and module outputs.
Repair or replace the confirmed failed component, then retest the system to ensure the code does not return.
