P2B99: Exhaust Pressure Control Valve A Driver Current/Temperature Too High

What it means

The output driver for the exhaust pressure control valve A reports current or junction temperature above its protection threshold. Stalled actuator or short-circuit fault.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

The ECM's output driver supplies and controls current to exhaust pressure control valve A's actuator, while monitoring driver temperature and current for protection. P2B99 sets when current draw or driver temperature exceeds its protection threshold, which can happen if the actuator is jammed or its control wire is shorted to ground.

Common causes

Most likely first.

1. Valve actuator mechanically jammed
2. Control wire shorted to ground

Symptoms

• Check-engine light

How to diagnose it

1. Save freeze-frame data and check for related actuator or supply codes to see when the valve A driver fault occurred.
2. Inspect valve A's actuator connector and control wiring for chafing, crushed insulation, corrosion, or a short to ground.
3. With the system safely de-energized as specified by the manufacturer, check whether valve A's mechanism is mechanically jammed or obstructed.
4. Test the actuator and control circuit for a short or abnormal current draw using the manufacturer's procedure and specification.
5. If the wiring and actuator pass their checks but the driver fault returns, follow the manufacturer's procedure to confirm an ECM output-driver fault.

Common fixes

• Repair a valve A control wire shorted to ground.
• Free or repair a mechanically jammed valve A actuator or mechanism.
• Replace the actuator if it draws excessive current despite free movement and sound wiring.
• Repair the ECM driver circuit only after confirming the actuator and wiring are within specification.

Can I keep driving?

The fault may place the vehicle in reduced-power mode even if the check-engine light is the only obvious symptom; avoid hard acceleration, high speeds, and towing. Arrange prompt diagnosis because an overloaded driver can disable valve A control and repeated current faults can worsen electrical damage.