Code
P1236
MINI
P — Powertrain
Fuel pump (FP) relay, primary circuit - high
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EN: 1
RU: 3
AI status
Completed
Completed
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Causes
- Short to battery (B+) in the relay control/harness
- Stuck or welded fuel pump relay contacts or internal relay fault
- Damaged connector or corroded terminals at the relay or body control module
- Open/incorrect ground or poor ground connection for the relay circuit
- Faulty PCM/ECM relay driver output
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
- Fuel pump runs continuously or does not operate correctly
- Engine cranks but no start, or intermittent starting
- Battery drain if relay is stuck closed
- Intermittent faults related to fuel pressure or pump operation
What to check
- Read freeze frame and active/inactive status with a scan tool; note when fault occurs (key ON, cranking, running)
- Visual inspection of relay, relay socket, wiring harness, and connectors for damage or corrosion
- Check related fuses and fusible links in power distribution
- Backprobe relay control and coil circuits with a DVOM or oscilloscope to observe voltages during key ON, crank, and run
- Measure coil resistance of the fuel pump relay and compare to spec (consult MINI service literature)
- Wiggle test harness while monitoring voltage to reproduce intermittent faults
Signal parameters
- Battery voltage (system): ~11.5–14.5 V (depending on engine/run state)
- Relay coil/control circuit expected: near 0 V when driven low (off) or near battery voltage when commanded high (on); consult service manual for exact logic
- Fault condition: control/primary circuit voltage higher-than-expected relative to commanded state (e.g., B+ present when it should be low)
- Coil resistance (typical relay): varies by relay — measure and compare to OEM spec
Diagnostic algorithm
- Safety: work in a well-ventilated area, isolate ignition source, and disconnect battery if required by procedures.
- Retrieve freeze frame and any related codes (e.g., fuel pump, battery, body control codes) to understand context.
- Visually inspect the fuel pump relay, relay socket, wiring harness, and power distribution center for melted plastic, corrosion, or damaged insulation.
- With ignition OFF, unplug the relay and inspect pins. Check for corrosion, pushed pins, or evidence of overheating.
- Measure relay coil resistance on the removed relay; compare to OEM spec. If suspect, substitute with known-good OEM relay and clear the code.
- With the relay reinstalled (or backprobing harness), use a DVOM or scope: monitor the relay primary/control terminal during key ON, crank, and run. Verify expected voltage transitions. Note if B+ appears when the circuit should be low.
- If B+ is present when it should be low, isolate the harness: disconnect connectors between relay and power source/ECM to find where B+ is coming from (check for short to B+).
- Check ground side continuity from relay ground to chassis ground and ensure low resistance.
- If wiring and connectors check good and substitution relay did not clear the code, test the PCM/ECM output driver following OEM procedures or consult dealer-level diagnostics.
- Repair or replace damaged wiring, connectors, relay, or PCM as indicated, then clear codes and road-test to confirm repair.
Likely causes
- Failed or stuck fuel pump relay
- Wiring short from relay control lead to battery positive (B+)
- Corroded or loose connector at the relay or fuse/relay box
- Faulty ground for relay coil circuit
- PCM/ECM output driver fault (less common)
Fault status
Status
DTC P1236 — Fuel pump relay primary circuit voltage high. The control module detected an unexpectedly high voltage on the fuel pump relay primary/control circuit. Investigate relay, wiring, connectors, ground, and module driver.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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