Code
P1187
CITROEN
P — Powertrain
Multifunction double relay control malfunction
Views:
UK: 3
EN: 10
RU: 5
AI status
Completed
Completed
100%
Causes
- Electrical fault in relay control circuit (open, short to ground or power)
- Defective multifunction double relay
- Blown or corroded fuse or connector
- Poor battery or supply voltage
- Control module (BCM/ECU) driver output fault
Symptoms
- MIL/Check Engine lamp illuminated
- Loss or intermittent operation of one or more accessories powered through the relay (e.g., fuel pump, fans, lighting circuits depending on application)
- Vehicle may not start or may stall if the relay controls critical systems
- Parasitic battery drain or unexpected fuse blows
- Intermittent electrical behavior correlated with engine off/on or vibration
What to check
- Read freeze frame and full DTC list with a capable scan tool; note related codes and live data
- Visual inspection of relay, fuse box, connector and wiring for corrosion, heat damage or loose pins
- Check battery voltage (12.4–12.8 V at rest) and charging system
- Verify fuse continuity and correct fuse(s) for the relay circuit
- Swap the suspect relay with an identical known-good relay (if available) and re-test
- Listen for relay click when circuit commanded; use a test light or scope to confirm switching
Signal parameters
- Battery supply to relay: ~12 V (vehicle off) to ~12.5–14.5 V (engine running)
- Control/coil activation voltage: near battery voltage when energized, ~0 V when not energized
- Coil resistance: expected closed-loop resistance specific to relay (refer to manufacturer specs)
- Driver output: ECU/BCM should switch to ground or +12 V as specified in wiring diagram; measure with DMM or scope
- Connector continuity to ground and battery: near 0 Ω to ground where applicable, low resistance between supply and relay feed
Diagnostic algorithm
- Connect scan tool, record the P1187 plus any other related codes and freeze frame data.
- Inspect fuse box, relay mounting area and connectors for corrosion, water ingress or heat damage; repair as needed.
- Verify battery and charging voltages; ensure stable supply during testing.
- Identify the multifunction double relay and its pinout from the wiring diagram/service manual.
- With ignition off, check fuse continuity and measure relay coil resistance. Compare to specification if available.
- With a helper or using the scan tool, command the circuit on and off while probing the relay coil feed and control pin for proper voltage change and ground switching.
- Check continuity between relay output pins and the loads they feed; inspect for shorts to ground or power.
- Swap the relay with a known-good identical relay (if possible) and clear codes to see if fault returns.
- If wiring and relay are good, test the control output from the BCM/ECU; if no driver action or wrong voltage, suspect module fault and confirm against manufacturer diagnostics before replacement.
- After repairs, clear codes, perform functional tests and a short road test to confirm the fault does not reappear.
Likely causes
- Failed multifunction relay (coil or contacts)
- Corroded or loose relay socket/connector pins
- Damaged wiring harness (chaffing, broken conductor, short)
- Blown fuse protecting the relay circuit
- Intermittent ground or poor battery main connection
- Faulty body control module or relay driver transistor
Fault status
Status
Manufacturer-specific DTC P1187 — Multifunction double relay control malfunction detected by the vehicle control unit.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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