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Home / DTC / P0687 — ECM/PCM Power Relay Control Circuit High

P0687 — ECM/PCM Power Relay Control Circuit High

Detailed page for trouble code P0687.

34,229codes
59brands
11,738generic
22,491specific
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Code

P0687

Generic P — Powertrain

ECM/PCM Power Relay Control Circuit High

Brand: Generic
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Short to battery voltage on the relay control wire
  • Failed or stuck power relay (contacts or internal coil short)
  • Open or corroded ground or poor ground connection at relay/PCM
  • Faulty PCM/ECM output driver
  • Blown/loose fuse supplying the relay coil or associated circuits
  • Wiring damage (chafing, corrosion, connector issues)

Symptoms

  • Malfunction Indicator Lamp (MIL) or stored DTC P0687
  • Intermittent or no crank/no start if relay fails to operate
  • Loss of PCM power to circuits or intermittent engine operation
  • Vehicle may run then shut off if relay control behaves erratically
  • Possible battery drain if relay is stuck closed

What to check

  • Read freeze frame and pending codes with a scan tool; record voltage and operating conditions
  • Visually inspect relay, relay socket, connectors and wiring for damage or corrosion
  • Check related fuses and power feeds for continuity and correct voltage
  • Back-probe the relay control terminal with key ON to measure voltage
  • Check for proper ground at relay socket and PCM ground connections
  • Swap the suspect relay with an identical known-good relay if available

Signal parameters

  • Relay coil supply: battery voltage (approximately 11–14.5 V) with key ON
  • PCM control output: expected near 0 V (ground) to energize relay; when off should be near battery voltage (~11–14.5 V) or high-impedance
  • Fault condition (High): control circuit measures battery/ignition voltage when it should be low; some systems report >5 V as ‘high’
  • Relay coil resistance typically tens to a few hundred ohms (manufacturer-specific)

Diagnostic algorithm

  1. Confirm P0687 is current; record freeze-frame and any related codes (P0562/P0563/P0627 etc.).
  2. Visually inspect the ECM/PCM power relay, socket and wiring for damage, corrosion, or loose terminals.
  3. With key ON (engine off), measure battery voltage at the relay supply terminal to verify proper feed (should be ~11–14.5 V).
  4. Back-probe the relay control terminal that connects to the PCM. With key ON and desired state (engine start or run depending on vehicle), verify control voltage: it should be low (~0–1 V) to energize. If it reads high (battery voltage), note the condition.
  5. Remove relay; check continuity of the control circuit from the relay socket back to the PCM connector. Inspect for short to battery on that wire (measure to battery positive) and for an open to PCM.
  6. Check ground integrity at relay ground and PCM ground points—measure resistance to battery negative; repair if high resistance.
  7. Swap the suspect relay with a known-good, identical relay and re-test to see if code clears or behavior changes.
  8. If wiring and relay are good but the control circuit still reads high at the PCM connector, suspect PCM output driver fault—verify with manufacturer procedures before replacing PCM.
  9. After repairs, clear codes and perform road/operation test to confirm fault does not return.

Likely causes

  • Shorted control wire to battery or ignition feed
  • Faulty power relay (stuck closed or internal short)
  • Poor ground at relay or PCM
  • PCM output driver failure

Fault status

⚠️ Status
P0687 — ECM/PCM Power Relay Control Circuit High: control circuit voltage above expected threshold (possible short to battery or relay/wiring fault).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

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Code

P0687

ISUZU P — Powertrain

ECM/PCM Power Relay Control Circuit High

Brand: ISUZU
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Short to battery voltage on the relay control wire
  • Failed or stuck power relay (contacts or internal coil short)
  • Open or corroded ground or poor ground connection at relay/PCM
  • Faulty PCM/ECM output driver
  • Blown/loose fuse supplying the relay coil or associated circuits
  • Wiring damage (chafing, corrosion, connector issues)

Symptoms

  • Malfunction Indicator Lamp (MIL) or stored DTC P0687
  • Intermittent or no crank/no start if relay fails to operate
  • Loss of PCM power to circuits or intermittent engine operation
  • Vehicle may run then shut off if relay control behaves erratically
  • Possible battery drain if relay is stuck closed

What to check

  • Read freeze frame and pending codes with a scan tool; record voltage and operating conditions
  • Visually inspect relay, relay socket, connectors and wiring for damage or corrosion
  • Check related fuses and power feeds for continuity and correct voltage
  • Back-probe the relay control terminal with key ON to measure voltage
  • Check for proper ground at relay socket and PCM ground connections
  • Swap the suspect relay with an identical known-good relay if available

Signal parameters

  • Relay coil supply: battery voltage (approximately 11–14.5 V) with key ON
  • PCM control output: expected near 0 V (ground) to energize relay; when off should be near battery voltage (~11–14.5 V) or high-impedance
  • Fault condition (High): control circuit measures battery/ignition voltage when it should be low; some systems report >5 V as ‘high’
  • Relay coil resistance typically tens to a few hundred ohms (manufacturer-specific)

Diagnostic algorithm

  1. Confirm P0687 is current; record freeze-frame and any related codes (P0562/P0563/P0627 etc.).
  2. Visually inspect the ECM/PCM power relay, socket and wiring for damage, corrosion, or loose terminals.
  3. With key ON (engine off), measure battery voltage at the relay supply terminal to verify proper feed (should be ~11–14.5 V).
  4. Back-probe the relay control terminal that connects to the PCM. With key ON and desired state (engine start or run depending on vehicle), verify control voltage: it should be low (~0–1 V) to energize. If it reads high (battery voltage), note the condition.
  5. Remove relay; check continuity of the control circuit from the relay socket back to the PCM connector. Inspect for short to battery on that wire (measure to battery positive) and for an open to PCM.
  6. Check ground integrity at relay ground and PCM ground points—measure resistance to battery negative; repair if high resistance.
  7. Swap the suspect relay with a known-good, identical relay and re-test to see if code clears or behavior changes.
  8. If wiring and relay are good but the control circuit still reads high at the PCM connector, suspect PCM output driver fault—verify with manufacturer procedures before replacing PCM.
  9. After repairs, clear codes and perform road/operation test to confirm fault does not return.

Likely causes

  • Shorted control wire to battery or ignition feed
  • Faulty power relay (stuck closed or internal short)
  • Poor ground at relay or PCM
  • PCM output driver failure

Fault status

⚠️ Status
P0687 — ECM/PCM Power Relay Control Circuit High: control circuit voltage above expected threshold (possible short to battery or relay/wiring fault).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0686 P0685 P0562 P0563 P0627
Repair manuals

Manual library for ISUZU

86

Browse 86 ISUZU manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

ISUZU

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Code

P0687

LAND ROVER P — Powertrain

engine control module / powertrain control module power relay control module - high circuit

Brand: LAND ROVER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Short to battery voltage on the relay control wire
  • Failed or stuck power relay (contacts or internal coil short)
  • Open or corroded ground or poor ground connection at relay/PCM
  • Faulty PCM/ECM output driver
  • Blown/loose fuse supplying the relay coil or associated circuits
  • Wiring damage (chafing, corrosion, connector issues)

Symptoms

  • Malfunction Indicator Lamp (MIL) or stored DTC P0687
  • Intermittent or no crank/no start if relay fails to operate
  • Loss of PCM power to circuits or intermittent engine operation
  • Vehicle may run then shut off if relay control behaves erratically
  • Possible battery drain if relay is stuck closed

What to check

  • Read freeze frame and pending codes with a scan tool; record voltage and operating conditions
  • Visually inspect relay, relay socket, connectors and wiring for damage or corrosion
  • Check related fuses and power feeds for continuity and correct voltage
  • Back-probe the relay control terminal with key ON to measure voltage
  • Check for proper ground at relay socket and PCM ground connections
  • Swap the suspect relay with an identical known-good relay if available

Signal parameters

  • Relay coil supply: battery voltage (approximately 11–14.5 V) with key ON
  • PCM control output: expected near 0 V (ground) to energize relay; when off should be near battery voltage (~11–14.5 V) or high-impedance
  • Fault condition (High): control circuit measures battery/ignition voltage when it should be low; some systems report >5 V as ‘high’
  • Relay coil resistance typically tens to a few hundred ohms (manufacturer-specific)

Diagnostic algorithm

  1. Confirm P0687 is current; record freeze-frame and any related codes (P0562/P0563/P0627 etc.).
  2. Visually inspect the ECM/PCM power relay, socket and wiring for damage, corrosion, or loose terminals.
  3. With key ON (engine off), measure battery voltage at the relay supply terminal to verify proper feed (should be ~11–14.5 V).
  4. Back-probe the relay control terminal that connects to the PCM. With key ON and desired state (engine start or run depending on vehicle), verify control voltage: it should be low (~0–1 V) to energize. If it reads high (battery voltage), note the condition.
  5. Remove relay; check continuity of the control circuit from the relay socket back to the PCM connector. Inspect for short to battery on that wire (measure to battery positive) and for an open to PCM.
  6. Check ground integrity at relay ground and PCM ground points—measure resistance to battery negative; repair if high resistance.
  7. Swap the suspect relay with a known-good, identical relay and re-test to see if code clears or behavior changes.
  8. If wiring and relay are good but the control circuit still reads high at the PCM connector, suspect PCM output driver fault—verify with manufacturer procedures before replacing PCM.
  9. After repairs, clear codes and perform road/operation test to confirm fault does not return.

Likely causes

  • Shorted control wire to battery or ignition feed
  • Faulty power relay (stuck closed or internal short)
  • Poor ground at relay or PCM
  • PCM output driver failure

Fault status

⚠️ Status
P0687 — ECM/PCM Power Relay Control Circuit High: control circuit voltage above expected threshold (possible short to battery or relay/wiring fault).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0686 P0685 P0562 P0563 P0627
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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+100 karma for a short comment :)
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