P0237

Turbocharger Boost Sensor A Circuit Low

P0237 is a generic OBD-II powertrain diagnostic trouble code: Turbocharger Boost Sensor A Circuit Low. It is logged by the engine control unit when the turbo/boost monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0237
Group
Powertrain
System
Turbo/Boost
Severity
Critical (limp mode / no-start)
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What P0237 means

P0237 is set when the ECM detects that the boost pressure sensor 'A' output voltage is below the minimum expected threshold — typically below approximately 0.5 V — while the engine is running. The sensor is a three-wire device supplied with a 5 V reference from the ECM; it returns a proportional voltage between about 0.5 V (atmospheric) and 4.5 V (maximum boost). A reading that drops below the lower limit indicates either a short to ground in the signal wire, an open in the reference voltage supply, a failed sensor, or a wiring fault that collapses the signal before it reaches the ECM input pin.

Because the ECM loses its ability to measure actual boost pressure, it cannot calibrate fuelling or manage the variable-geometry turbo (VNT) vanes or wastegate accurately. The vehicle typically enters a severe limp mode with boost capped at a minimal level, producing a pronounced power deficit. On diesel engines, this often manifests as very poor acceleration above idle, heavy black smoke (excessive fuelling without boost feedback), or an inability to rev beyond a low ceiling. The fault is present from the moment the signal drops and the MIL illuminates immediately.

P0237 is closely related to P0238 (circuit high) and P0236 (rationality). Common on European vehicles equipped with Bosch, Siemens, or Delphi engine management systems, particularly BMW, Audi, Volvo, and VAG diesel platforms. Damaged wiring harnesses near the turbocharger — where heat and vibration are greatest — are a frequent root cause.

Common causes

Most-frequently reported root causes when P0237 is logged.

  • 1
    Short to ground on the boost sensor signal wire, pulling the output below the ECM minimum voltage threshold.
  • 2
    Open circuit in the 5 V reference supply wire between the ECM and the sensor, causing the sensor output to collapse.
  • 3
    Internally failed boost sensor with a shorted sensing element producing a near-zero output.
  • 4
    Damaged wiring harness near the turbocharger — heat, chafing against the exhaust or engine block, or vibration cracking the insulation.
  • 5
    Corroded, spread, or pushed-back terminal in the boost sensor connector causing high resistance or loss of continuity.
  • 6
    Open ground circuit for the sensor producing an offset shift that can push the signal below threshold.
  • 7
    ECM sensor input circuit failure (rare — diagnose only after ruling out all external wiring and sensor faults).

Symptoms drivers notice

Check Engine Light illuminated, often immediately at startup.
Severe power loss or limp mode — engine restricted to low rpm and boost, particularly noticeable above 2,000 rpm.
Rough idle or unusually low idle on diesel engines caused by incorrect fuelling without boost feedback.
Possible audible turbocharger noise changes if the ECM defaults to a fixed VNT/wastegate position.
Increased exhaust smoke (typically black on diesel) due to fuelling without accurate boost pressure data.

How to diagnose P0237

A typical diagnostic flow when this code is present.

  1. 1
    Scan the ECM, record freeze frame data, and note any companion codes (P0236, P0238, MAP sensor faults).
  2. 2
    With the ignition on and the engine off, measure the boost sensor signal wire voltage at the sensor connector — it should read approximately 0.5–0.7 V; a reading at or near 0 V confirms a short to ground or open reference supply.
  3. 3
    Check the 5 V reference wire at the sensor connector; if absent, trace back to the ECM to locate the open or short.
  4. 4
    Inspect the wiring harness along its route near the turbocharger for heat damage, chafing, melted insulation, or broken shielding.
  5. 5
    Disconnect the sensor and measure resistance between the signal pin and chassis ground — any reading below 10 kΩ with the sensor disconnected points to a wiring short.
  6. 6
    Substitute a known-good boost sensor; if voltage returns to normal range, replace the original sensor.
  7. 7
    Clear codes, perform a road test under load with live boost sensor data displayed, and confirm no fault recurrence.

Related powertrain codes

Frequently asked questions

Why does P0237 cause such severe power loss?

Without a credible boost pressure signal, the ECM cannot manage boost safely. To avoid the risk of turbocharger overspeed or engine over-boost, it defaults to a minimal fixed pressure value and caps fuelling and VNT/wastegate control accordingly. The result is that the turbo essentially stops contributing meaningful power.

How do I tell P0237 from P0236?

P0237 means the signal voltage is below the sensor's electrical floor (typically <0.5 V) — a hard electrical fault. P0236 means the voltage is within electrical bounds but the pressure it implies disagrees with other sensors — a rationality or calibration fault. P0237 usually points to a short to ground or open reference; P0236 more often points to contamination, a boost leak, or sensor drift.

Can a boost leak cause P0237?

A boost leak alone will not drive the signal voltage below 0.5 V and therefore will not set P0237 directly. A boost leak causes the sensor to report unexpectedly low (but valid) pressure, which is more likely to trigger P0236. P0237 requires an electrical fault in the sensor circuit itself.

Is it safe to drive with P0237 active?

No. The ECM is operating without accurate boost pressure data, and while limp mode protects the engine from over-boost, driving in this state risks misfires, catalytic converter damage from unburnt fuel, and erratic turbocharger behaviour. The vehicle should be towed or driven only minimally to a workshop.

Disabling P0237 in software

RaceTune can permanently disable P0237 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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