P1574

Code

MINI P — Powertrain

Engine control module (ECM), sensor supply circuit B - high output

Brand: MINI

Type: P — Powertrain

Views: UK: 1 EN: 1 RU: 0

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Page language: EN

Short circuit from sensor supply B wire to constant battery voltage (B+)
Open or high-resistance ground for ECM or sensor supply return
Faulty ECM (internal regulator or monitoring circuit)
Damaged wiring harness or corroded connector contacts on sensor supply B circuit
Aftermarket electrical equipment or incorrect jump-start/charging connections causing over-voltage
Intermittent connector contact or water ingress causing spurious readings

Read freeze-frame and readiness monitors; note any additional sensor codes
Visually inspect wiring and connectors for damage, corrosion, or water entry along sensor supply B harness
Confirm battery voltage and charging system condition (rule out high system voltage)
Locate fuse(s) and relays for sensor supply circuits; check fuse integrity and correct value
Backprobe the sensor supply B reference pin at the ECM and at representative sensors with ignition ON (engine OFF)
Measure continuity/resistance from supply B pin to battery positive and to ground (with ignition OFF, battery disconnected as required)

Expected sensor reference voltage (B) with ignition ON, engine OFF: approximately 5.0 V (typical tolerance 4.8–5.2 V).
Measured voltage significantly above reference (e.g., >5.5 V or near battery voltage) is out of range.
With ignition OFF, supply B should read approximately 0 V (no backfeed).
Resistance from sensor supply B pin to ECM ground should be very low (a few ohms to tens of ohms depending on harness length); high resistance suggests connection issue.
No significant voltage drop (≥0.5 V) should occur between ECM supply pin and sensor connector under key ON conditions.

Retrieve and record all stored codes and freeze-frame data. Note which sensors are on supply B.
Visually inspect harnesses, connectors and junction points for sensor supply B from ECM to sensors; repair any obvious damage.
With key OFF, disconnect battery if required by service manual before repairing wiring or connectors.
With key ON (engine OFF), backprobe the ECM sensor supply B terminal and a sensor supply B terminal. Compare voltages; both should be ~5 V. If one reads high (near battery voltage) and the other normal, suspect a short near the high-reading side.
If supply B reads high at the ECM connector, disconnect all sensors on that circuit. Re-check the voltage at the ECM. If high remains, suspect ECM or fused feed short to B+; if it returns to normal, reconnect each sensor one at a time to find the faulty component.
Check for a short to battery voltage by measuring resistance from supply B conductor to B+ with battery disconnected. Low resistance indicates a short.
Check grounds related to the ECM and sensor circuits. Repair/clean grounding points and re-test.
If wiring and connectors check good and short to B+ not found, test or replace ECM as last resort per manufacturer's procedures (follow immobilizer/programming precautions).
Clear codes and perform a road test/drive cycle to verify the fault does not return and that all related sensors operate normally.

⚠️ Status

Engine control module reports sensor supply circuit B voltage higher than allowable threshold (sensor reference circuit B - high output).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours

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P1574 — Engine control module (ECM), sensor supply circuit B - high output