P2AC9: Charge Air Cooler Coolant Temperature Sensor B Circuit Low

What it means

Voltage on the charge air cooler coolant temperature B sensor signal line is below the expected window. Wire shorted to ground or sensor short.

At a glance

• Usually lights the check-engine light

How it works

Charge air cooler coolant temperature sensor B sends a voltage signal representing the coolant temperature. The control module sets this code when that signal falls below its expected range, commonly because the signal is pulled toward ground or the sensor is internally shorted.

Common causes

Most likely first.

1. Signal wire shorted to ground
2. Internal sensor short
3. Connector pins corroded - high contact resistance

Symptoms

• Check-engine light may be on
• Reduced engine power
• Poor acceleration, especially under load

How to diagnose it

1. Record freeze-frame data and read sensor B's live temperature; a reading far outside plausible temperatures can support a low-signal fault.
2. Inspect sensor B's connector for corrosion, moisture, bent pins, or terminals pushed out of position.
3. Follow the sensor B harness and check for chafing or crushed insulation that could let the signal wire contact ground.
4. With the circuit isolated as directed by the vehicle wiring information, check the signal wire for a short to ground.
5. Test sensor B and its supply and ground circuits against the manufacturer's specification to distinguish a shorted sensor from a wiring fault.

Common fixes

• Clean and secure corroded or loose sensor B connector terminals.
• Repair the signal wire where it is shorted to ground or damaged.
• Replace charge air cooler coolant temperature sensor B if it fails the specified circuit test.

Can I keep driving?

A short, gentle trip may be possible if the engine runs normally, but avoid heavy acceleration and towing because the control module may limit power. Stop if power loss becomes severe or the engine behaves abnormally.