P0691 2018 GMC Sierra Code - Cooling Fan Speed Output Circuit Low Voltage
Quick Answer
The engine cooling fan system is composed of 2 electric cooling fans, fan motors, and 2 control modules. Common causes include Faulty Cooling Fan Control Module, Cooling Fan Control Module harness is open or shorted, Cooling Fan Control Module circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
- What it means
- P0691 2018 GMC Sierra indicates Cooling Fan Speed Output Circuit Low Voltage.
- Common causes
- Common causes include Faulty Cooling Fan Control Module, Cooling Fan Control Module harness is open or shorted, Cooling Fan Control Module circuit poor electrical connection.
- Severity
- High - diagnose this code as soon as possible.
- Can I drive?
- Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Code P0691 2018 GMC Sierra Description
The cooling fan speed is affected by many different conditions and the ECM will adjust the duty cycle from 0 - 100 percent based on cooling system requirements. The scan tool output control is only capable of operating the cooling fan increments, between 10 - 90 percent. 90 percent is considered high-speed fan. When multiple cooling fan speed requests are received, the ECM operates the fan at the highest speed requests.
The Diagnostic Trouble Code (DTC) will be set when the commanded state of the driver and the actual state of the control circuit do not match for greater than 5 s.
What are the Possible Causes of the DTC P0691 2018 GMC Sierra?
- Faulty Cooling Fan Control Module
- Cooling Fan Control Module harness is open or shorted
- Cooling Fan Control Module circuit poor electrical connection
- Faulty Engine Control Module (ECM)
How to Fix the DTC P0691 2018 GMC Sierra?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P0691 2018 GMC Sierra code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
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Frequently Asked Questions about P0691 2018 GMC Sierra Code
1. What does the OBDII code P0691 mean on a 2018 GMC Sierra?
P0691 indicates a low voltage issue in the cooling fan speed output circuit, which controls the fan's operation to prevent the engine from overheating.
2. What are the common symptoms of the P0691 code in a 2018 GMC Sierra?
Symptoms can include the engine running hotter than normal, the cooling fan not operating, or the Check Engine Light illuminating.
3. What causes the P0691 code to appear in a 2018 GMC Sierra?
Common causes include a faulty cooling fan relay, a damaged cooling fan motor, wiring issues such as shorts or open circuits, or a malfunctioning Engine Control Module (ECM).
4. How do I troubleshoot the P0691 code on my 2018 GMC Sierra?
Start by inspecting the cooling fan relay, fan motor, and related wiring for damage or loose connections. Use a multimeter to check for proper voltage and continuity in the circuit.
5. Can I drive my 2018 GMC Sierra with the P0691 code active?
It’s not recommended, as the cooling fan may not function properly, potentially leading to engine overheating and significant damage.
6. How is the P0691 code typically fixed on a 2018 GMC Sierra?
Repairs may include replacing a faulty cooling fan relay, repairing or replacing damaged wiring, replacing a defective fan motor, or reprogramming or replacing the ECM if necessary.
7. How much does it cost to fix the P0691 code on a 2018 GMC Sierra?
Repair costs can vary but generally range from $100 to $500, depending on whether the issue is with the relay, wiring, fan motor, or ECM.
8. Can a blown fuse cause the P0691 code in a 2018 GMC Sierra?
Yes, a blown fuse in the cooling fan circuit can result in low voltage and trigger the P0691 code.
9. How can I prevent the P0691 code from recurring in my 2018 GMC Sierra?
Regular maintenance, including checking the cooling fan system and associated wiring for wear or damage, can help prevent this issue.
10. Will clearing the P0691 code with a scan tool fix the issue in a 2018 GMC Sierra?
Clearing the code may turn off the Check Engine Light temporarily, but the underlying issue must be repaired to prevent the code from returning.
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