P1636

Code

DS P — Powertrain

Supply relay control short circuit to positive

Brand: DS

Type: P — Powertrain

Views: UK: 2 EN: 7 RU: 2

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Page language: EN

Damaged or shorted wiring between ECU and supply/ignition relay (insulation rubbed through, chafing to B+)
Stuck or welded relay contact internally feeding control circuit with B+
Faulty relay socket or terminal shorted to battery positive
Poor or corroded ECU connector pins causing unintended contact with B+
Internal ECU/PCM driver transistor or relay-driver component fault
Aftermarket accessory or incorrect wiring tied into the relay/control circuit

Malfunction Indicator Lamp (MIL) or warning lamp illuminated
Intermittent or no power to systems that are switched by the supply/ignition relay (engine cranking/start faults, ECU power issues)
Blown fuses related to ignition/supply circuits
Vehicle may enter limp mode, have no-start, or random shutdowns
Battery draining when ignition is off in severe shorts

Visually inspect relay and relay socket for corrosion, melted plastic, or signs of heat
Inspect wiring harness along the route for chafing, pinched wires, or repair splices near bodywork or bulkheads
Check related fuses for damage and for signs of overheating
Verify connector pins at the ECU and relay are straight, clean and properly seated
Disconnect aftermarket accessories that may tap into the relay or B+ circuit

Battery voltage (B+): ~12.0–14.5 V with engine off/charging respectively
Relay control output (ECU pin) expected: near 0 V when inactive, pulled to B+ when commanded ON (unless open/low-side driver design)
If fault present: control pin measures near B+ when it should be low (indicates short to positive)
With relay unplugged: control pin should not be permanently at B+ if driver is functioning (may be 0 V or toggle with command)
Continuity: control wire to relay coil terminal should show low resistance when measuring between relay socket and coil (with ignition off)

Read freeze frame and live data; confirm P1636 is present and note ignition/state when set.
Visually inspect relay, socket, harness and fuse box for heat damage, melting, or evidence of B+ contact.
With ignition off, disconnect the supply/ignition relay. Measure voltage at the ECU relay-control pin: it should not be at full battery voltage when the relay is unplugged. If it is at B+, suspect wiring short to B+ or internal ECU fault.
Backprobe relay socket control terminal with relay removed. Check continuity to battery positive. There should not be a direct short to B+. If there is continuity to B+, trace wiring and repair short.
Wiggle test the harness while monitoring the control pin for intermittent changes; repair chafed areas or replace damaged sections.
Swap in a known-good relay (same type) and see if code clears and function returns. If swapping fixes it, replace relay and inspect socket.
If wiring and relay check OK and control pin still reads incorrectly, test ECU driver output per manufacturer procedure (use scope if available) or consult dealer-level diagnostics; replace ECU only after confirming internal driver failure.
After repairs, clear codes and perform a drive/test cycle to ensure P1636 does not return.

⚠️ Status

Supply relay control — short circuit to positive (control circuit sees unexpected battery voltage).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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P1636 — Supply relay control short circuit to positive