Diesel Trouble Codes

P0237 — Turbocharger/Supercharger Boost Sensor A Circuit Low — LLY / LBZ / LMM Duramax

P0237 on LLY/LBZ/LMM Duramax means the ECM sees the boost (MAP) sensor signal voltage below its valid range. On this platform the boost sensor is the MAP…

Updated October 15, 2026

What it means

Generic definition: ECM sees the boost (MAP) sensor signal voltage below its valid range. Platform note: LLY/LBZ/LMM Duramax 2004.5–2010 use a MAP sensor for boost monitoring; the turbo is a Garrett GT3788VA VGT with hydraulic vane control and vane position feedback.1

Most likely causes

  1. MAP sensor signal shorted to ground or wiring harness chafed/open causing low voltage at ECM — Inspect the MAP/boost sensor connector and wiring for opens, shorts to ground, or chafing; check reference and signal circuits for continuity and proper voltage. Typical on this platform to check the boost sensor connector and wiring for an open or short to ground, then the sensor.1
  2. Failed MAP/boost pressure sensor internal fault pulling signal low — Sensor internal failure can bias the signal low. Verify sensor supply, ground, and signal voltage with a scan tool and multimeter; compare to known-good values.1
  3. ECM input circuit fault or connector corrosion causing low signal reading — Corrosion or moisture at the ECM or sensor connector can create a low bias on the signal line. Inspect connectors, clean and re-seat, and check ECM pin for proper reference voltage and ground.1

How to diagnose

  1. Verify code and freeze frame; confirm P0237 is present and note engine conditions at set.
  2. Visually inspect MAP/boost sensor and wiring harness for damage, oil contamination, or chafing; pay attention to areas near the intake and firewall.
  3. Disconnect the MAP sensor and inspect terminals for corrosion or bent pins; check connector lock and seal.
  4. Key on, engine off: measure MAP sensor reference voltage and ground at the sensor connector; compare to spec.
  5. Backprobe the MAP signal wire and measure voltage key on, engine off and at idle; a voltage below valid range indicates a low circuit.
  6. Check continuity from MAP sensor signal pin to ECM pin and inspect for shorts to ground along the harness.
  7. If wiring and connector are good, substitute a known-good MAP/boost sensor and retest for code return.
  8. Clear codes, road test under load to verify boost builds and MAP readings track expected values.
  9. If code persists with good sensor and wiring, evaluate ECM input circuit per manufacturer diagnostics.

Parts and tools you may need

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Shop diagnosis—1–2 hrsShop
Wiring or connector repair$10–$1001–4 hrsDIY with tools and a manual
MAP/boost pressure sensor$40–$2000.3–1 hrsEasy DIY

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 tests are inconclusive, or the ECM input is suspect, have a qualified diesel technician perform pin-out and ECM diagnostics. Do not attempt high-pressure fuel system service without proper training and safety equipment.

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

  1. Curated DTC seed — LLY / LBZ / LMM Duramax (curated) ↩︎ ↩︎ ↩︎ ↩︎

Repair videos: P0237 on the LLY-LMM Duramax

Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.

2005 GMC Duramax (LLY) Map Sensor replacement #Duramax #GMC — Ben Jacobs · 44K views

LLY Duramax MAP vs Barometric Pressure Sensor – Location & How to Tell Them Apart — Boosted Motorsports 2 · 1K views