P0237 — Turbocharger/Supercharger Boost Sensor A Circuit Low — 5.9 Cummins 24-Valve (VP44)

Diagnostic guide for P0237 on 5.9 Cummins 24-Valve VP44 (1998.5–2002).

Updated October 15, 2026

What it means

The ECM sees the boost (MAP) sensor signal voltage below its valid range. On the 5.9L 24-valve the turbo is a fixed-geometry Holset HX35/HY35, so this is a sensor-circuit fault: a failed boost sensor, an open or grounded signal wire, or a connector fault.¹

Most likely causes

1. Boost (MAP) sensor failed internally, pulling signal low — Sensor internal fault causing low output voltage to ECM.¹
2. Signal wire open or shorted to ground between sensor and ECM — Wiring/connector damage causing low voltage on signal circuit.¹
3. Boost sensor connector corroded, loose, or oil-contaminated — Poor connection at sensor raises resistance or grounds signal.¹

How to diagnose

1. Inspect boost sensor connector for corrosion, oil, or loose terminals; repair as needed.
2. Check sensor supply (5 V reference) and ground at the sensor connector with key on; verify correct voltages.
3. Back-probe sensor signal wire and compare voltage at idle and with engine running to spec; low voltage indicates sensor or wiring fault.
4. Disconnect sensor and check ECM side for short to ground on signal wire; repair wiring if shorted.
5. If wiring and power/ground are good, replace boost sensor and retest.
6. Clear codes and road test to confirm repair.

Parts and tools you may need

• Digital multimeter
• Back-probe pins
• Dielectric grease
• Replacement boost/MAP sensor
• Wiring repair kit

Tools you’ll need

• digital multimeter — Checks 5 V reference, ground, and signal voltage at the MAP sensor connector to confirm low signal and wiring integrity.
• back-probe kit — Allows safe measurement of the MAP signal wire voltage at idle and under boost without damaging the connector.
• OBD-II scan tool — Reads P0237 and live MAP/boost data to verify sensor output and confirm repair after replacement.
• electrical contact cleaner — Cleans oil/corrosion from the boost sensor connector before testing and after repair.

Rough cost and difficulty

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If wiring faults are found in the harness or ECM connector, or if code returns after sensor replacement, have a diesel technician inspect the harness and ECM inputs. Do not attempt high-pressure fuel system work.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources