Diagnosing Po66a Glow Plug Circuit Low
When your car’s engine light comes on with a PO660A fault code, it’s a clear indication that the glow plug control circuit is malfunctioning, causing a “glow plug control circuit low” issue. This problem can lead to poor engine performance, decreased fuel efficiency, and potentially even engine damage if left unchecked. The PO660A code is a common issue that can affect various vehicles, and it’s essential to diagnose and repair it as soon as possible to avoid further complications.
The PO660A fault code is triggered when the glow plug control circuit detects a low voltage or an open circuit condition. This can be caused by a faulty glow plug, a malfunctioning glow plug control module, or a wiring issue. The symptoms of a glow plug control circuit low issue can include a failing cold start, rough engine idling, and decreased engine performance.
Po66a Fault Code Glow Plug Control Circuit Low
The Po66A fault code is a troubleshooting indicator that signals an issue with the glow plug control circuit. This code is typically displayed on the vehicle’s onboard diagnostics (OBD) system and is usually accompanied by a warning light on the dashboard. The glow plug control circuit is responsible for regulating the glow plugs, which are essential for starting the engine, especially in cold temperatures. The Po66A fault code can be caused by several factors, including: Corrosion raises resistance, which can cause the glow plug control circuit to malfunction. Water damage can also lead to electrical issues, while burnt or faulty glow plugs can prevent the engine from starting. The ECU plays a crucial role in regulating the glow plug control circuit, and any issues with the ECU can lead to the Po66A fault code. In this section, we will explore the causes and symptoms of the Po66A fault code, as well as provide guidance on how to diagnose and troubleshoot the issue. Importance of proper diagnosis: Proper diagnosis is crucial in resolving the Po66A fault code issue. Improper repair or replacement of components can lead to further damage and costly repairs. It is essential to use a code reader or scan tool to retrieve the trouble codes and perform a thorough inspection of the glow plug control circuit. Next steps: In the next section, we will discuss the symptoms of a glow plug control circuit low issue and provide guidance on how to identify the problem.
Symptoms Of A Glow Plug Control Circuit Low Issue
A malfunctioning glow plug control circuit can result in poor engine starting, rough engine idle, and decreased fuel efficiency. The issue may also cause the glow plugs to not heat up properly, leading to a decrease in engine performance. This can be a significant problem, especially in cold weather.
- Engine Performance Issues: A low battery voltage or a faulty glow plug control circuit can cause the engine to start rough or stall. This is because the glow plugs are not getting the necessary power to heat up the engine.
When the glow plug control circuit is low, it can also cause the engine to overheat, as the glow plugs are not providing the necessary heat to warm up the engine. This can lead to a decrease in engine performance and potentially cause damage to the engine.
It’s essential to address the issue promptly to prevent further damage to the engine. A malfunctioning glow plug control circuit can also cause the engine to not start, especially in cold weather.
Diagnostic Tests For The Po66a Fault Code
Diagnosing a low glow plug control circuit starts with a scan tool to confirm the code and check for related faults. The PCM logs PO66A when it detects voltage below the expected threshold at the glow plug control module, so live data and freeze-frame readings are essential. Most late-model diesel trucks – especially Ford 6.7L Power Stroke, GM Duramax, and Ram Cummins – use a dedicated glow plug control module that communicates over the CAN bus, so a generic OBD-II scanner may not show enough detail.
For example, a Ford F-250 with a 6.7L engine may store PO66A alongside U-codes for CAN bus errors, while a Duramax might show a P-code for glow plug performance. Always record freeze-frame data before clearing codes, as it captures engine conditions when the fault occurred, like coolant temperature, RPM, and battery voltage.
Visual Inspection
Start under the hood with the engine off and the key out of the ignition. Wear safety glasses and disconnect the negative battery cable before touching any wiring.
Glow Plug Testing
Testing individual glow plugs requires a digital multimeter and a glow plug socket. Disconnect the glow plug harness before testing to avoid false readings.
Pro Tip: On 2013-2019 Ram 6.7L Cummins engines, the glow plug control module is integrated into the engine control module (ECM). If PO66A appears, the ECM may need to be replaced – an expensive repair that requires dealer-level software to program.
Possible Causes Of The Po66a Fault Code
Corrosion raises resistance by forming a barrier between the glow plug and the circuit, preventing the control module from sending the correct signal to the glow plug. This can occur due to moisture, dirt, or other contaminants that seep into the engine compartment. Additionally, a faulty glow plug or a dirty glow plug socket can also cause the PO66A fault code.
Other possible causes of the PO66A fault code include a malfunctioning glow plug control module, a faulty coolant temperature sensor, or a wiring issue between the control module and the glow plug.
In some cases, the PO66A fault code can be caused by a combination of factors, such as a faulty glow plug and a malfunctioning glow plug control module. It’s essential to diagnose the issue thoroughly to determine the root cause of the problem.
Repair Options For The Po66a Fault Code
Replacing the faulty glow plug control circuit module is the primary solution to address the Po66a fault code. This module, often referred to as the glow plug control module or GPCM, is responsible for managing the glow plug circuit and ensuring proper operation. The GPCM is usually located near the engine or in the fuse box, and its replacement can be done with basic tools and mechanical skills. When replacing the GPCM, it’s essential to ensure that the new module is compatible with the vehicle’s make and model. Additionally, the replacement process may require specific tools, such as a scan tool, to reset the system and clear the fault code. System Repair In some cases, the Po66a fault code may be caused by a more complex issue, such as a short circuit or a malfunctioning sensor. In these situations, a system repair may be necessary to identify and address the underlying problem. It’s crucial to exercise caution when working with electrical systems, as shorts or other malfunctions can lead to more severe issues, such as engine damage or fires. Important Considerations When repairing the Po66a fault code, it’s essential to consider the following factors: The age and condition of the vehicle The cost and availability of replacement parts The potential impact on the vehicle’s performance and reliability The expertise and tools required for the repair By understanding these factors and taking the necessary precautions, you can ensure a successful repair and avoid more costly problems down the road.
Cost Breakdown For Repairing The Po66a Fault Code
Repair costs for this circuit fault vary significantly based on whether the issue stems from a simple wiring break or a failed glow plug control module. Most owners should budget between $150 and $600 for a professional repair, depending on the specific vehicle make and labor rates in their area.
Labor And Parts Investment
Labor charges typically account for the majority of the bill because diagnosing electrical gremlins requires time with a multimeter and wiring diagrams. A technician usually spends one to two hours tracing the circuit to pinpoint the exact location of the low voltage signal. Independent shops often charge between $100 and $180 per hour, while dealerships may exceed that rate.
Parts pricing fluctuates based on the complexity of the glow plug system integration. Some vehicles use a standalone control module that is easy to replace, while others integrate the control logic into the engine computer or a complex relay block. OEM parts always provide the best reliability for these sensitive electronic components.
| Component | Estimated Part Cost | Estimated Labor Time |
|---|---|---|
| Diagnostic Fee | N/A | 1.0 – 2.0 Hours |
| Glow Plug Module/Relay | $80 – $250 | 0.5 – 1.0 Hour |
| Wiring Harness Repair | $20 – $100 (Materials) | 1.0 – 3.0 Hours |
| Fuse/Fusible Link | $5 – $20 | 0.2 – 0.5 Hour |
Pro Tip: Always ask the shop to perform a voltage drop test on the wiring before replacing the control module. Many shops see a low circuit code and immediately throw a module at the problem, but a corroded ground wire is a much cheaper fix that often gets overlooked.
For instance, if a rodent has chewed through a section of the harness, the parts cost remains minimal, but the labor hours climb quickly as the technician strips back loom and repairs individual wires. Conversely, a failed module is a quick swap, but the component itself carries a higher price tag. Verify if your vehicle has a TSB (Technical Service Bulletin) regarding this specific code, as some manufacturers have updated parts or wiring kits that resolve common failures more permanently.
Prevention Of The Po66a Fault Code
Glow plug control circuits fail most often from corrosion, vibration, and voltage spikes. Diesel engines in humid climates or frequent short-trip drivers see the highest failure rates within 60,000 to 80,000 miles. Regular maintenance that targets these conditions can extend circuit life by 30-50%.
Regular Maintenance
Replace glow plugs in sets every 60,000 miles, even if only one fails. Mixing old and new plugs creates uneven resistance that strains the control module. Use OEM or premium aftermarket plugs – Bosch Duraterm or NGK Y-1001 are proven choices for most Ford, GM, and VW diesels.
Electrical System Checks
Voltage spikes from failing alternators or weak batteries are the second-leading cause of control module damage. A $30 multimeter (Innova 3320) lets you verify system voltage during cranking and idle.
For example, a 2015 Ford F-250 owner avoided repeated Po66a codes by replacing the alternator’s voltage regulator after noticing 14.8-volt spikes during highway driving. The fix cost $120 in parts and 45 minutes of labor – far less than the $450 module replacement that would have followed.
Diesel engines with block heaters should have their power cords inspected monthly. Frayed cords short to the engine block, sending voltage surges through the glow plug circuit. A $20 cord replacement (ZeroStart 3100200) prevents this hidden failure point.
Pro tip: If your diesel sits for more than a week, disconnect the battery negative terminal. Parasitic draws from the glow plug control module can drain batteries in as little as 10 days, especially in cold weather.
Quick Summary
Experiencing a po66a fault code indicates a glow plug control circuit issue, which may require professional diagnosis and repair to prevent engine damage.
| Code | Description |
|---|---|
| po66a | Glow plug control circuit low |
Frequently Asked Questions
What Does A Po66a Fault Code Indicate About My Engine?
A PO66A fault code typically indicates a problem with the glow plug control circuit, which is a critical system for cold-starting your engine. This can be a serious issue, and it’s essential to have it diagnosed and repaired by a professional mechanic as soon as possible.
Can I Drive My Car With A Po66a Fault Code?
It’s not recommended to drive your car with a PO66A fault code, as it can cause damage to your engine or even lead to a no-start situation. However, if you’re far from a repair shop, you can try to limp your car to a safe location, but do not drive it at high speeds or for an extended period.
How Much Will It Cost To Repair A Po66a Fault Code?
The cost to repair a PO66A fault code can vary depending on the age and make of your vehicle, as well as the complexity of the repair. On average, you can expect to pay between $200 to $1,000 for the necessary repairs, including replacement parts and labor.
Can I Replace The Glow Plug Control Module Myself?
While it’s possible to replace the glow plug control module yourself, it’s not a recommended DIY project, especially if you’re not familiar with your vehicle’s electrical system. If you’re not comfortable with the repair, it’s best to leave it to a professional mechanic who has the necessary expertise and experience.
What Are The Symptoms Of A Faulty Glow Plug Control Circuit?
The symptoms of a faulty glow plug control circuit can include difficulty starting the engine, rough engine performance, and decreased fuel efficiency. In some cases, you may also notice a specific diagnostic trouble code (DTC) on your car’s onboard diagnostic (OBD) system, such as PO66A.
Will Repairing A Po66a Fault Code Affect My Car’s Warranty?
Repairing a PO66A fault code may affect your car’s warranty if the repair is not done by an authorized dealership or a reputable independent mechanic. Be sure to check your warranty documentation and consult with your mechanic to ensure that the repair does not void your warranty.
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