What is the difference between P0237 and P0238?

They are opposite ends of the same fault. P0237 means the boost sensor's signal is stuck too low, and typically points at a short to ground or an open in the signal circuit. P0238 means the signal is stuck too high, and typically points at a short to voltage or a lost sensor ground, either of which pulls the signal up toward reference voltage. The diagnostic tools are the same — live data, a mechanical pressure comparison, and circuit testing — but what you are hunting for is reversed, so reading the code correctly saves real time.

Why did my car lose all its power with P0238?

Because the PCM cannot tell a false high signal from real overboost, and real overboost can destroy an engine through detonation. Faced with a boost reading it has no reason to trust, the computer takes the safe option: it caps boost, closes the throttle, and drops into a reduced-power mode. The engine can be mechanically perfect and still refuse to pull, because the protection is acting on bad data. Restoring a correct signal normally returns full power immediately, which is why the sensor circuit is worth fixing promptly rather than living with.

Could P0238 mean my turbo really is overboosting?

It can, and that case is worth ruling out because it carries real risk. If the sensor is accurate and boost genuinely is climbing past target, the cause is usually a wastegate that will not open — a stuck flapper, a failed actuator, or a disconnected control line — and continued hard driving risks detonation and engine damage. In practice true overboost is more often captured by P0234. The clean way to separate the two is to compare the sensor's live data against a mechanical gauge on the intake under load. If they disagree, the circuit is lying. If they agree, go look at the wastegate.

Can a bad ground cause P0238?

Yes, and it is one of the most commonly missed causes. These sensors output a voltage between ground and the 5-volt reference. If the ground path is open, corroded, or high in resistance, there is nothing holding the signal down and it drifts up toward reference voltage — which reads as a circuit-high fault even though the sensor itself is fine. Testing the ground for continuity and low resistance takes a few minutes with a multimeter and costs nothing, so it belongs early in the process rather than after a new sensor has already been fitted.

OBD-II trouble code

P0238: Turbocharger/Supercharger Boost Sensor "A" Circuit High

The boost pressure sensor signal is reading above its expected window. Despite the 'turbocharger' name this is a sensor-circuit code — the usual causes are a short to voltage, an open ground, or a failed sensor, and the PCM will often cut power to protect the engine because it cannot tell a false high reading from real overboost.

Medium severityPowertrainFuel & AirDrivable short-term

Quick facts

System: Powertrain
Category: Fuel & Air
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $100 – $900
DIY difficulty: Intermediate DIY

What does P0238 mean?

The boost pressure sensor — sometimes a dedicated sensor in the charge piping, sometimes the manifold absolute pressure sensor doing double duty — reports how much pressure the turbocharger or supercharger is producing in the intake. The PCM uses that number to control boost, to protect against overboost, and to set fueling and timing. P0238 sets when the signal from boost sensor "A" stays above the expected range: the circuit-high condition.

P0238 is the direct opposite of P0237. P0237 means the signal is stuck too low; P0238 means it is stuck too high. That distinction matters because it changes what you are looking for. A circuit-low fault is typically a short to ground or an open in the signal wire. A circuit-high fault is typically a short to voltage — the signal wire touching the 5-volt reference or a battery-voltage circuit — or a lost or high-resistance ground, which pulls the signal up toward reference voltage because there is nothing holding it down. A failed sensor stuck at the top of its range does the same thing. On sensors that read pressure through a hose, a reference line routed to a pressurized source or a sensor exposed to boost when it should see manifold vacuum can also read high.

The important consequence for the driver is that the PCM cannot distinguish a falsely high signal from genuine overboost, and genuine overboost destroys engines. So its response is conservative: it commonly limits boost, closes the throttle, or drops into a reduced-power limp mode. That is why P0238 so often shows up as a sudden and dramatic loss of power rather than as a quiet check engine light. The engine may be mechanically perfect and still refuse to make power, because the computer is acting on a number it has no reason to trust.

There is a real case that should not be dismissed, though. If the sensor is accurate and boost genuinely is climbing too high, you have an overboost condition, and the mechanical cause behind it — a wastegate that will not open, a stuck linkage, a failed actuator, a disconnected control line — is a problem that can cause detonation and engine damage. In practice P0234 is the code that normally captures true overboost, and P0238 is more usually electrical. The way to tell them apart is to compare the sensor's live data against actual measured pressure. If the sensor claims 20 psi and a mechanical gauge on the intake shows 8, the sensor or its circuit is lying. If both agree that boost is high, stop chasing wiring and go look at the wastegate.

Diagnosis therefore starts with that comparison, then moves to the circuit: check the signal wire for a short to voltage, verify the ground is clean and low-resistance, confirm the 5-volt reference is correct, inspect the connector for corrosion and pushed-out pins, and check any pressure reference hose for correct routing and condition. Replace the sensor only once the circuit, the reference, and the actual pressure all point at it.

Common causes

Short to voltage in the boost sensor signal wire, often against the 5-volt reference
Open, corroded, or high-resistance sensor ground pulling the signal up
Failed boost/MAP pressure sensor stuck at the high end of its range
Corroded, loose, or water-intruded sensor connector
Pressure reference hose routed to the wrong source or exposed to boost instead of manifold pressure
Chafed harness where the signal wire has worn through against a bracket or the engine
Incorrect or wrong-range replacement sensor fitted
Genuine overboost from a wastegate stuck closed, which the sensor is honestly reporting
PCM internal fault on the sensor input, rare and diagnosed last

Symptoms

Check engine light with P0238 stored
Sudden and significant loss of power, often the first thing the driver notices
Reduced-power or limp mode that caps boost regardless of throttle input
Hesitation, surging, or flat throttle response
Poor fuel economy from the PCM's fallback fueling strategy
Boost reading in live data noticeably higher than a mechanical gauge shows
Black smoke or a rich condition on some diesel applications

Diagnostic steps

1.Read the boost sensor's live data with the key on and the engine off. At rest it should report roughly barometric pressure. A value pegged high with no boost being made points immediately at the sensor or its circuit.
2.Compare the sensor's reported boost against actual pressure measured with a mechanical gauge under load. Disagreement means the circuit is lying; agreement means boost really is high and the wastegate is the target.
3.Inspect the connector for corrosion, water intrusion, and pushed-out or spread pins.
4.Check the sensor ground for continuity and low resistance. A lost ground is one of the most common causes of a circuit-high code and costs nothing to test.
5.Verify the 5-volt reference is present and correct at the sensor connector.
6.Disconnect the sensor and check whether the signal wire is shorted to voltage, then inspect the harness run for chafing against brackets and engine components.
7.On hose-referenced sensors, confirm the reference line is routed to the correct source and is not cracked, pinched, or oil-soaked.
8.Back-probe the signal wire and watch the voltage while wiggling the harness to catch an intermittent short.
9.If everything electrical checks out and actual boost is genuinely high, move to the wastegate, its actuator, and the boost control solenoid.
10.Replace the sensor only after the ground, reference, signal wire, connector, and reference hose have all been verified good.

Repair cost

$100 – $900

A boost or MAP pressure sensor replacement typically runs $100-$350 with labor, since the sensor is usually accessible in the charge piping or on the intake. A wiring, ground, or connector repair can be cheaper — sometimes under $150 — and a misrouted or cracked reference hose is close to free. Diagnosis alone commonly runs $100-$180 because separating a false signal from real overboost takes a mechanical pressure comparison rather than just a code read. The upper end applies where a chafed harness has to be traced and repaired properly, or where the reading turns out to be honest and the underlying overboost fault requires wastegate or actuator work.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.