P2B91: Turbocharger/Supercharger B Temperature Sensor Circuit High

What it means

The ECM detects a circuit high fault on the turbocharger/supercharger b temperature sensor. Reading cannot be used reliably for control.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The turbocharger/supercharger B temperature sensor sends a temperature signal to the ECM. P2B91 sets when the signal is higher than the usable range, commonly because the signal circuit is open or shorted to battery voltage; the ECM cannot rely on that reading.

Common causes

Most likely first.

1. Signal wire shorted to B+
2. Open sensor
3. Connector pins corroded - high contact resistance

Symptoms

• Check engine light on

How to diagnose it

1. Save freeze-frame data and compare the B sensor reading with other temperature readings from a cold start; an implausibly high value can help identify a circuit-high fault.
2. Inspect the B sensor connector and harness for corrosion, loose terminals, broken wires, or damage that could leave the signal circuit open or expose it to battery voltage.
3. Check the B sensor signal circuit for a short to B+ and verify continuity using the vehicle wiring diagram.
4. Check the sensor connector terminals and the sensor reference and ground circuits for poor contact or an open.
5. Test the B temperature sensor against the manufacturer's specification and replace it if it is open while the wiring is sound.

Common fixes

• Clean or repair corroded or loose terminals at the B temperature sensor connector.
• Repair an open in the B sensor signal wiring.
• Repair a signal wire shorted to B+.
• Replace the B temperature sensor if it tests open.

Can I keep driving?

If the check-engine light is the only symptom, a short, gentle trip may be possible; avoid heavy boost or towing until the fault is checked. An unreliable B temperature reading can impair engine control and emissions, even if no power loss is apparent.