Code
P1188
PEUGEOT
P — Powertrain
Multifunction double relay control malfunction
AI status
Completed
Completed
100%
Causes
- Failed multifunction (double) relay
- Corroded, loose or damaged relay socket/connector
- Broken, shorted or high-resistance wiring in the relay control or supply circuit
- Blown fuse supplying the relay or ECU
- Poor battery or ground connection causing low supply voltage
- Faulty ECU relay driver/output transistor
Symptoms
- Malfunction Indicator Lamp (MIL) or warning light illuminated
- Intermittent or no start / hard start
- Engine stalls or cuts out unexpectedly
- Multiple electrical loads (fuel pump, ignition, accessories) not operating
- Blown fuses or recurring fuse failures
- Random loss of engine power or electrical functions
What to check
- Read stored freeze-frame and fault history with a capable scan tool; note conditions when fault set
- Visually inspect relay, relay socket, connectors and wiring for corrosion, heat damage or loose pins
- Check fuses and fusible links related to the relay and ECU
- Swap relay with a known-good identical relay (if available) to test function
- Measure battery voltage at battery and at relay supply terminal with key ON
- Measure relay coil/control voltage at connector while operating (key ON/crank or commanded by scanner)
Signal parameters
- Nominal battery supply: ~12 V with engine off, 13.5–14.5 V charging when running
- Relay coil control: switched 0 V (ground) or +12 V depending on design; should change state when commanded
- Relay coil resistance: typically tens to a few hundred ohms (vehicle-specific) — compare to service spec
- Control signal type: ON/OFF (low-side or high-side driver); in some systems may be PWM/duty-cycle controlled
- Expected current draw through coil: typically 0.1–1 A (check component spec)
Diagnostic algorithm
- Connect a diagnostic scanner, read codes and freeze-frame. Confirm P1188 is current or historic and note conditions.
- Perform a visual inspection of relay, socket, harness, and related fuses. Repair any obvious damage or corrosion.
- With ignition ON, verify battery voltage at relay supply terminal. Replace weak battery/repair charging if voltage out of range.
- Swap the suspect multifunction relay with an identical known-good relay. Re-scan for P1188 and test symptoms.
- Backprobe relay coil/control terminals while commanding the relay with a scan tool or cycling ignition. Verify proper control voltage and switching.
- Check continuity between relay control terminal and ECU driver pin. Repair any opens/shorts or high resistance.
- Inspect/measure ground circuits for the relay and ECU. Clean and secure any poor grounds.
- If harness, fuse and relay test good but driver signal absent or abnormal, perform ECU output driver tests per manufacturer procedure. Consider ECU replacement only after all external causes are ruled out.
- Clear codes and road-test to confirm repair. Monitor for recurrence and any related codes.
Likely causes
- Relay contacts stuck or coil open/shorted
- Connector pins corroded or pushed out of housing
- Open/short between ECU relay output and relay coil
- Fuse supplying relay is open
- ECU internal driver has failed after harness and relay checks
Fault status
Status
ECU detected malfunction in multifunction double relay control circuit. Possible causes include faulty relay, wiring/connector issue, blown fuse, low supply voltage, or ECU driver failure. Further inspection and testing required.
Repair difficulty: Medium
Diagnostic time: 0.5 - 2.0 hours
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