P0237 Code: Turbocharger/Supercharger Boost Sensor A Circuit Low

What the P0237 code means

The sensor measures the pressure the turbo builds in the intake. The computer uses it to control the wastegate or the variable geometry of the turbo. If the signal is not valid, the computer usually limits boost for safety.

The P0237 code is stored when the computer detects that the signal is below its minimum value, from a short to ground or a missing 5 volt reference. The sensor works with a 5 volt reference, a ground and a signal that should vary between about 0.5 and 4.5 volts. The extreme values, near 0 volts or near 5 volts, are reserved for detecting faults. A signal that sits at either extreme does not match any real position or pressure.

With the engine off, the sensor should read atmospheric pressure and match the barometric sensor. When you accelerate under load, it should climb smoothly up to the pressure the computer is asking for. Oil that comes through the crankcase vent and soot from the EGR dirty the sensor port, and that is a common cause of bad readings on diesels.

Remember that the code tells you where the computer saw the problem, not which part is broken. Use the sensor testing steps below to find the real fault.

P0237 code symptoms

• Check engine light on, and sometimes the power reduced light as well.
• Loss of power because the computer limits the turbo.
• Lack of push when accelerating.
• Other related codes from the same sensor.

Likely causes of the P0237 code

1. Signal wire shorted to ground from the harness rubbing on the engine, the body or a metal bracket.
2. 5 volt reference open or shorted. It is often shared with other sensors, so if several of them set codes at once, the fault is in the common reference.
3. Damaged sensor with an internal short that pulls the signal to ground.
4. Connector with moisture. Water between the pins creates a path to ground.

How to diagnose the P0237 code step by step

1. Read the signals on the scan tool and compare them with the other sensors or with the commanded pressure.
2. Inspect the connector. Look for green, backed-out or oily pins and check that the lock is closed.
3. Check 5 volts and ground at the connector with the key on: 4.8 to 5.1 volts on the reference and less than 0.1 volt of drop on the ground.
4. Measure the signal with the connector plugged in while you move the pedal or throttle, or accelerate for a turbo. It should change smoothly, with no jumps and no drops to zero.
5. Do a wiggle test with the engine running. Move the harness and watch the reading.
6. Check continuity of each wire back to the computer with the key off. It should be under 1 ohm.
7. Compare boost pressure and barometric pressure with the engine off and the key on. They should match.
8. Check the intercooler hoses and clamps. A leak changes the real pressure and throws off the diagnosis.

How to fix the P0237 code

• Repair the connector or the wiring.
• Replace the sensor. On electronic throttle systems this is normally the pedal or the whole throttle body.
• Check the hoses and pressure ports of the turbo.
• Clear the codes and confirm the repair with a road test.

Technical reference data

• 5 volt reference, ground and a signal of roughly 0.5 to 4.5 volts.
• Engine off: atmospheric pressure, about 100 kPa (14.5 psi) at sea level.
• At full load: 150 to more than 250 kPa absolute (about 22 to 36 psi), depending on the engine.
• These are reference values only. Check the manufacturer data for your engine.

Brand-specific notes

On diesels, the turbo pressure sensor often includes the intake air temperature sensor, and oil from the crankcase vent can foul it. If you see the P0237 code on a high mileage diesel, clean the port before you spend money on parts.

Frequently asked questions about P0237