P0240: Second boost sensor not reading as expected
Turbocharger boost sensor B circuit range/performance
Severity: Inspect soon
Kelley Blue Book says P0240 can send the engine into limp mode with limited speed and no A/C, so it should be checked soon.
P0240 in short
P0240 means the computer sees the second turbo boost pressure sensor reading outside the expected range. A failed or contaminated sensor, bad connector or an exhaust leak is the usual cause. It can trigger limp mode with reduced power, so get it checked soon.
Turbocharged engines use boost pressure sensors so the computer can manage fuel and turbo output. Sensor B is a second sensor, sometimes for a second turbo.
TaT describes P0240 as a plausibility fault: the reading is in range electrically but does not match what the engine is doing.
Kelley Blue Book lists a failing sensor, electrical connection problems, contamination and exhaust leaks that make the signal fluctuate.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Failed or contaminated boost pressure sensor
Common general cause- Why it ranks here
- KBB lists sensor failure and contamination first.
- What would change this
- Rises if the reading is stuck or disagrees with sensor A. Falls if the readings match.
Cause 2: Electrical connection problem at the sensor
Common general cause- Why it ranks here
- KBB lists electrical connection issues.
- What would change this
- Rises if the connector is loose or corroded. Falls if the connection is fine.
Cause 3: Exhaust or boost leak causing fluctuating readings
Possible — needs testing- Why it ranks here
- KBB says exhaust leaks can make the boost signal fluctuate.
- What would change this
- Rises if a leak is heard. Falls if the system holds pressure.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read live boost readings from all boost sensors and compare them.
IfSensor B disagrees with sensor A at rest
It meansSuspect sensor B or its wiring.
IfThey agree
It meansThe fault may be intermittent; check for leaks.
Step 2: Inspect sensor B connector and look for boost or exhaust leaks.
Warning:Keep clear of the hot turbo and exhaust.
IfConnector corroded or loose
It meansRepair and retest.
IfA leak is found
It meansRepair it.
Points to: Exhaust or boost leak causing fluctuating readings
IfNeither found
It meansReplace the sensor.
Symptoms
- Check engine light
- Limp mode: low power and limited speed Gets more serious: stop and have it checked.
- Poor fuel economy
Compare with: Check engine light with loss of power
How to fix
On your vehicle
We don't have reviewed vehicle-specific evidence for P0240 yet. The causes and tests above apply across vehicles.
Related codes
No curated relationships for P0240 yet.
P0240 questions
What does boost sensor B mean?
It is the second boost pressure sensor, for instance on a second turbo, the computer compares with sensor A.
Sources and review
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
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