What it means
The monitored signal in the high-voltage interlock circuit for battery charging system A is above its expected range.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The high-voltage interlock loop for battery charging system A tells the vehicle whether the protected charging connections are securely closed. The module monitors the loop signal and sets P0D18 when it reads higher than the expected range, which can happen if the signal wire is shorted to power or the loop's pull-down path is open.
Common causes
Most likely first.
- Wire shorted to B+
- Pull-down resistor open
- Connector pins corroded - high contact resistance
Symptoms
- Charging system warning light may come on
- Charging may be interrupted or unavailable
- Vehicle may limit high-voltage operation
How to diagnose it
- Read freeze-frame data and related charging or interlock codes to see when system A's signal went high and whether charging was active.
- With the vehicle powered down as specified by the manufacturer, inspect system A's interlock connectors and harness for corrosion, loose pins, or damage that could connect the signal to power.
- Check the interlock connector terminals for corrosion or poor contact, since added contact resistance can distort the monitored signal.
- Using the wiring diagram, test the interlock signal wire for an unintended short to B+ and check the pull-down path for an open.
- Compare circuit readings and interlock status with the manufacturer's specification, then repair the fault and confirm the signal remains in range.
Common fixes
- Clean or repair corroded interlock connector terminals.
- Repair a damaged signal wire shorted to B+.
- Repair an open pull-down resistor or its wiring.
- Replace a failed interlock circuit component if testing identifies it.
Can I keep driving?
Avoid charging and limit high-voltage driving if the vehicle warns that charging is unavailable or restricts operation; the interlock fault can interrupt charging or trigger reduced-power operation. Follow the vehicle's shutdown procedure before inspecting high-voltage components.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.