What does it mean?
P04A2 is the opposite electrical condition to a low circuit fault on the same valve. The module watches its driver output for the second exhaust pressure control valve and finds the voltage still sitting high at a moment when energising the load should have pulled it down. Two very different faults create that picture: an open circuit, where no current can flow because a wire, terminal or winding is broken, and a short to battery voltage, where an outside supply holds the line up regardless of what the driver does. The module cannot tell those two apart on its own, so it stores one code for both and disables the output. Because the valve never actuates, the functions that depend on backpressure are lost until the circuit is repaired.
Symptoms
- MIL (check engine lamp) illuminated and the function disabled
- Very slow warm up and poor cabin heat, the same complaint as a stuck open valve
- Aftertreatment regeneration that never reaches its target temperature
- Scan tool actuation produces no valve movement and no click or motor sound
- Additional codes for warm up performance or exhaust temperature appearing over time
Likely causes
- Broken or disconnected wire between the control module and the valve, including a terminal backed out of the connector
- Open solenoid or motor winding inside the valve after a thermal failure
- Corroded, burned or spread terminal in the valve connector creating a high resistance joint
- Control wire chafed against a positive feed or a battery supply line, shorting to battery voltage
- Blown fuse or open relay contact on the supply side of the valve, so the load side never pulls down
- Damaged connector lock allowing the plug to sit partly seated after previous service work
- Module driver stage failed open, confirmed only after external wiring tests pass
How to fix it
- Check whether the code is current, then attempt to actuate the valve with a scan tool while listening and watching for movement
- Back probe the valve connector with the ignition on and measure voltage on both pins; system voltage on both sides usually means an open on the ground or control leg
- Measure valve winding resistance across the terminals; an infinite reading confirms an internally open valve
- Perform a continuity check on the control wire from the module connector to the valve, and a separate check for unintended voltage on that wire with the valve unplugged
- Inspect connector terminals for corrosion, heat discoloration, spread contacts and terminals pushed out of their locks
- Verify the fuse and any relay that feeds the valve, since an open supply mimics this fault exactly
- Repair the wiring or replace the valve based on what the measurements show, then clear the code and confirm the valve responds to commands