P0285: Cylinder 9 Injector A Circuit Low

What does P0285 mean?

P0285 means the control wire of the cylinder 9 injector – the side the engine module switches to ground – is shorted to ground. GM detects this with the driver off: on direct injection at 1 V or less, on port injection and Duramax diesels at 0.5 Ω or less to ground. Ford's 6.7 diesel has its driver chip report the short within 0.3 s. Most systems switch the warning light on in the first trip (some GM port-injection engines and Saab's 2.0 turbo after two) and shut the affected injector off, so the cylinder misfires. Ford petrol engines report all injector circuit faults as P0201 ff instead. Cylinder 9 exists only on ten-cylinder engines; no manufacturer document using this code was found – Ford's V10 uses P0201–P0210 and GM has no V10 – so the description follows CARB and the codes for cylinders 1–8.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light on
• Misfire and rough running, misfire code P0309
• Loss of power, rough idle
• Injector shut off, limp mode possible on diesels

Common causes

• High Control wire of the cylinder 9 injector chafed to ground in the harness
• Medium Injector connector damp or corroded, leakage to ground
• Medium Injector shorted to its housing internally
• Low Open control wire (on some GM port-injection drivers this also reads low; P020x sets too)
• Low Driver stage in the engine module faulty

Likelihood is a general estimate across vehicles; your make and model may differ.