P0238 — Turbocharger/Supercharger Boost Sensor A Circuit High — 7.3 Power Stroke
P0238 Turbocharger/Supercharger Boost Sensor A Circuit High
What it means
The PCM sees the boost (MAP) sensor signal voltage above its valid range. On the 7.3L Power Stroke this is usually a failed MAP sensor or a signal wire shorted to the 5 V reference.1
Most likely causes
- Failed MAP sensor producing high voltage output — The MAP sensor on the 7.3L reads intake manifold pressure via a small hose. Internal failure can drive the signal high.1
- Signal wire shorted to 5 V reference or power — A chafed or pinched MAP signal wire can pull the voltage up out of range.1
- Corroded or damaged MAP sensor connector causing reference short — Connector corrosion can bridge the signal to the 5 V reference circuit.1
- MAP sensor hose issue affecting sensor reading — A cracked, plugged with oil/soot or loose MAP hose can cause implausible readings; inspect hose condition as part of boost-sensor diagnostics.2
- Unplugged or corroded MAP connector — A poor connection can cause the PCM to see an out-of-range high voltage.3
How to diagnose
- Verify code and freeze-frame conditions; confirm P0238 is present and note engine speed/load at set.
- Key-on, engine-off: compare MAP voltage/pressure to barometric pressure; a high reading at KOEO points to sensor or wiring.
- Inspect MAP sensor and its small vacuum hose from the intake; check for cracks, oil/soot plugging, looseness, and proper routing.
- Inspect MAP sensor connector and wiring for corrosion, oil contamination, chafing, and pin damage; check for shorts to 5 V reference or power.
- Disconnect MAP sensor and check PCM-side voltage on signal pin with key-on; compare to expected 5 V reference and ground integrity. Do not probe high-pressure oil systems.
- Reconnect sensor and monitor live MAP voltage/pressure at idle and during a controlled load increase; look for voltage stuck high or out of plausible range.
- If MAP reads high with sensor disconnected, suspect wiring short to voltage; if reading normal with sensor disconnected but high with sensor connected, suspect sensor failure.
Parts and tools you may need
- Digital multimeter
- Scan tool with live data
- Basic hand tools for sensor access
- Dielectric grease
- Replacement MAP sensor and vacuum hose as needed
Tools you’ll need
- digital multimeter — Measures KOEO MAP signal voltage and checks for a short to 5 V reference on the PCM side with the sensor disconnected.
- OBD-II scan tool — Reads P0238, freeze-frame data, and monitors live MAP voltage/pressure at idle and under load to confirm a stuck-high reading.
- inspection mirror — Lets you see the MAP sensor and its small vacuum hose on the 7.3L intake for cracks, oil/soot plugging, and routing without removing components.
- terminal release tool set — Safely opens the MAP connector to inspect pins for corrosion/oil and to check wiring for chafing or shorts to reference/power.
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 |
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 engine harness or the PCM reference voltage is abnormal, have a qualified diesel technician diagnose and repair the harness/PCM circuits. Do not attempt repairs on high-pressure oil systems. If the vehicle shows 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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