P0687
UniversalECM/PCM Power Relay Control Circuit High
High SeverityThis code indicates that the voltage in the control circuit for the ECM/PCM power relay is higher than expected. This can prevent the ECM/PCM from receiving proper power, leading to engine no-start conditions or unexpected stalling while driving.
⚠️ Before You Begin (Safety First)
Always disconnect the battery before working on electrical components to prevent electrical shock or damage to the vehicle's systems. Ensure the vehicle is safely parked with the parking brake engaged before commencing any repairs.
Common Symptoms
- Check Engine Light illuminated
- Engine cranks but will not start
- Engine stalls unexpectedly while driving
- Intermittent engine operation
- No power to the ECM/PCM
Common Causes
- Faulty ECM/PCM power relay
- Short to voltage in the ECM/PCM power relay control circuit
- Open circuit within the power relay control circuit wiring
- Corroded or loose connections at the relay or ECM/PCM
- Faulty ECM/PCM (less common)
Frequently reported on: General/Universal
Diagnostic Steps
- Retrieve all stored diagnostic trouble codes and freeze frame data using an OBD-II scanner.
- Locate the ECM/PCM power relay in your vehicle's fuse box; consult your owner's manual or a service manual for its exact location.
- Visually inspect the ECM/PCM power relay and its connections for any signs of corrosion, burning, or damage.
- Test the functionality of the ECM/PCM power relay. This can often be done by swapping it with a known good, identical relay from a non-critical system (e.g., horn relay) to see if the symptoms change.
- Using a multimeter, check for proper voltage and ground signals at the relay's socket according to the vehicle's wiring diagram.
- Inspect the wiring harness leading to the ECM/PCM power relay for any signs of shorts to voltage or open circuits. Pay close attention to areas where wiring might be rubbed or pinched.
- Clear the P0687 code and retest the system to see if the code returns.
👨🔧 When to Call a Professional
If you're uncomfortable testing electrical circuits with a multimeter or cannot locate the fault after basic checks, it's best to consult a professional automotive electrician, especially if the problem is intermittent or involves complex wiring harnesses. Do not attempt to bypass relays or wiring without proper knowledge, as this can cause significant damage.
Commonly Asked Questions
What is the ECM/PCM power relay?
The ECM/PCM power relay is an electrical switch that controls the flow of power to your vehicle's engine control module (ECM) or powertrain control module (PCM). It ensures the computer receives the necessary voltage to operate.
Can I drive my car with a P0687 code?
No, it is not advisable to drive with a P0687 code. This code indicates a critical power supply issue to the ECM/PCM, which can lead to your engine failing to start or stalling unexpectedly, creating a hazardous driving situation.
How can I test the ECM/PCM power relay at home?
You can test the relay by first visually inspecting it for damage. Then, you can swap it with an identical, known-good relay from another non-critical system in your vehicle. If the problem resolves, the relay was likely faulty. For a more thorough test, use a multimeter to check for continuity across the relay's terminals when activated with an external power source.
What does 'Control Circuit High' mean in this context?
'Control Circuit High' typically means that the voltage detected in the relay's control circuit is above the specified operating range. This could be due to a short circuit to a constant voltage source, an open circuit, or an internal fault within the relay itself.
Is it possible the ECM/PCM itself is faulty?
While a faulty ECM/PCM is a possibility, it is generally less common than a bad relay or wiring issue. It's crucial to thoroughly diagnose the relay and all associated wiring and connectors before considering ECM/PCM replacement, as this is a costly repair.