P0687 — ECM/PCM Power Relay Control Circuit High

P0687 — ECM/PCM Power Relay Control Circuit High. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: control module driver fault, faulty sensor or actuator of the affected circuit, blown fuse feeding the circuit.

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P0687 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the ECM/PCM power relay control for damage, corrosion, chafing or poor contact.
Subsystem check With the ECM/PCM power relay control disconnected, measure signal voltage at the harness connector: a high reading with the component unplugged indicates a short to power in the harness; if it drops to normal, the component itself is faulty.
Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P0687 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P0687 (parts and labor, USD, independent shop rates): Repair wiring or connectors: $80–$250; Control module repair: $300–$1,000; Replace the faulty sensor or actuator: $150–$500. Overall, fixing P0687 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What are the symptoms of P0687?

Drivers most often notice: the affected system operates intermittently or not at all, increased fuel consumption in some cases, Check Engine Light on, possible limp mode depending on the affected component.

Is it safe to drive with P0687?

In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How do I diagnose P0687 myself?

Start with a scan: confirm P0687, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the ECM/PCM power relay control, and verify the suspect component against live data before buying parts.

How much does it cost to fix P0687?

Repair wiring or connectors — $80–$250; Control module repair — $300–$1,000; Replace the faulty sensor or actuator — $150–$500. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What does OBD2 code P0687 mean?

When your OBD2 scanner pulls a P0687 code, it tells you the engine control module has detected that the relay controlling its own power supply is stuck in an "on" position. The official definition reads "ECM/PCM Power Relay Control Circuit High," and it falls under the powertrain category since it affects engine and transmission management systems.

The phrase "circuit high" indicates that the voltage present on the ECM/PCM power relay control wire has climbed above its normal operating range — typically hovering near full battery voltage when it should be switching on and off. This abnormal reading points to one of three scenarios: the relay control circuit has shorted directly to a power source, a ground connection has broken somewhere in the control path, or a component has failed in a way that forces the signal line high regardless of the module's commands. The engine computer doesn't trigger this code based on a single bad reading; it waits until the condition repeats under specific operating conditions before illuminating the check engine light. The freeze frame data stored alongside P0687 is valuable — it records engine load, RPM, coolant temperature, and vehicle speed at the exact moment the fault occurred, which helps you recreate the problem during diagnosis.

Symptoms of P0687

The system the relay controls runs intermittently or stops functioning entirely
Fuel economy may drop noticeably in some vehicles
Check Engine Light remains illuminated
Vehicle may enter reduced-power limp mode depending on which subsystem is affected
Some vehicles experience no-start conditions if the ECM loses proper relay control
Auxiliary electrical systems may shut down unexpectedly

What Causes P0687?

The most common culprit behind P0687 is a failed ECM or PCM power relay that forces the control circuit high. Beyond that, the fault typically traces to one of several electrical problems. An open ground return prevents the control module from properly switching the relay, leaving the circuit in a high state. A signal wire that has shorted to battery positive bypasses the module's control entirely. Damaged wiring anywhere in the circuit — whether from wear, heat damage, or rodent interference — creates similar symptoms. The control module's internal driver transistor can fail, losing its ability to ground the relay control circuit. Downstream components like sensors or actuators that share the affected circuit can also develop internal shorts. A blown fuse upstream removes ground reference entirely. Corroded connectors introduce resistance that disrupts proper switching, while loose or damaged terminals create intermittent opens that confuse the module.

How to Diagnose P0687

Before beginning any testing, connect your OBD2 scanner and confirm P0687 is the active code, then record all freeze frame data — this snapshot tells you precisely what conditions existed when the module detected the fault. Review any other stored codes as well, since related failures often share a common root cause. Check for any manufacturer technical service bulletins (TSB) specific to your vehicle's make, model, and model year; many P0xxx codes have documented factory fixes or software updates that resolve the issue without physical repairs.

Perform a thorough visual inspection of all wiring and connectors associated with the ECM/PCM power relay control circuit. Look for frayed insulation, broken strands, corrosion buildup, and any signs of overheating or melted wiring. With the power relay disconnected from the control module, probe the harness side of the connector with a multimeter. If you still read high voltage with the component unplugged, the short exists in the wiring harness itself. If the voltage drops to normal reference levels, the fault lies within the relay or associated component.

Test reference voltage, ground integrity, and signal continuity directly at the component connector using your multimeter and wiring diagram. For an even more thorough check, perform a wiggle test on the harness while monitoring live data on your scanner — any signal dropouts indicate broken wires that only fail under movement. Once repairs are complete, clear the code, run the vehicle through a complete drive cycle including the specific conditions from your freeze frame data, and verify that P0687 does not return.

Repair Options for P0687

The most cost-effective approach targets the simplest and most common failures before considering expensive component replacement. Wiring harness repairs or connector replacement typically run between $80 and $250 including labor and materials. If the ECM/PCM power relay itself has failed internally, control module repair or replacement costs fall in the $300 to $1,000 range depending on whether your vehicle requires dealer programming. When a faulty sensor or actuator further down the circuit has caused the short, replacement runs $150 to $500 for parts and installation.

Total Cost to Fix P0687

Actual repair costs hinge entirely on which component has failed. Here are typical scenarios at independent shop rates in USD: wiring or connector repair runs $80–$250, control module service or replacement costs $300–$1,000, and sensor/actuator replacement runs $150–$500. In most cases, addressing P0687 costs between $80 and $1,000 total. The key to avoiding unnecessary expense is accurate diagnosis before purchasing parts — the priciest repair option is rarely where you should start, and a thorough electrical inspection often pinpoints the problem without guessing wrong on major components.

Can You Drive with P0687?

P0687 carries a short-term severity rating, meaning most vehicles remain driveable but with potential performance limitations or disabled auxiliary systems. However, if the fault causes stalling, prevents the engine from starting, or triggers warnings related to braking or steering assist, treat the situation as urgent and seek repair immediately.