P0237 — Turbocharger/Supercharger Boost Sensor A Circuit Low — 5.9 Cummins Common Rail
Diagnostic reference for 5.9 Cummins Common Rail 2003-2007 (ISB 5.9 common rail).
What it means
The ECM sees the boost (MAP) sensor signal voltage below its valid range. On the 5.9L common rail this is a MAP sensor circuit low condition, not a mechanical underboost code.1
Most likely causes
- MAP sensor connector or wiring open/short to ground — Inspect the MAP sensor connector and wiring for an open or short to ground; check for corrosion, chafing, or loose terminals.1
- Faulty MAP sensor — A failed MAP sensor can pull the signal low. Verify sensor supply voltage and ground, then compare sensor output to a known-good reference under key-on and idle conditions.1
- Boost reference hose to MAP sensor leaking, cracked, or clogged — A damaged or disconnected reference hose can cause an erroneous low reading at the sensor. Inspect the hose and fittings for cracks, oil contamination, or blockage.2
How to diagnose
- Verify code and freeze-frame data; confirm P0237 is present and note engine speed, load, and temperature at set.
- Key-on, engine-off: check MAP sensor supply voltage and ground per service information; confirm 5 V reference and good ground.
- Inspect MAP sensor connector and wiring for corrosion, moisture, or chafing; repair as needed.
- Inspect boost reference hose to MAP sensor for cracks, leaks, oil saturation, or blockage; replace if compromised.
- Monitor live MAP sensor voltage with a scan tool while idling and during a light acceleration; compare to expected values for barometric and idle boost.
- If voltage remains low with harness disconnected from sensor, suspect wiring short to ground; isolate harness and test continuity to ECM.
- If wiring tests good, substitute a known-good MAP sensor and retest; persistent low voltage points to ECM or harness issue.
Common mistake to avoid
Replacing the turbo before smoke-testing the intake. Boost leaks at intercooler boots, end tanks and clamps are a common cause of low power and underboost codes, and they mimic a failing turbo. Source: BD Diesel — 6.7L Power Stroke problems and real fixes.
Parts and tools you may need
- Digital multimeter
- Scan tool with live data
- Basic hand tools
- Replacement MAP sensor
- Replacement boost reference hose and clamps
Tools you’ll need
- OBD-II scan tool — Reads P0237 and live MAP voltage to confirm low signal and compare to expected barometric/idle values.
- Digital multimeter — Checks 5 V reference, ground, and sensor signal voltage key-on/engine-off and isolates wiring shorts to ground.
- Hand vacuum/pressure pump with gauge — Tests the MAP boost reference hose and sensor port for leaks, cracks, or blockage affecting signal.
- Inspection light — Reveals corrosion, moisture, chafing, or oil saturation at the MAP connector and boost hose.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| Wiring or connector repair | $10–$100 | 1–4 hrs | DIY with tools and a manual |
| MAP/boost pressure sensor | $40–$200 | 0.3–1 hrs | Easy DIY |
| Intercooler boot, clamp or pipe repair | $20–$200 | 0.5–2 hrs | Easy 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 good and a known-good MAP sensor does not correct the low signal, have the ECM and harness evaluated by a qualified diesel technician. Do not attempt high-pressure fuel system service. If the vehicle exhibits drivability issues, have it inspected promptly.
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
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