P065D Reductant System Malfunction Lamp Control Circuit

The engine module switches this hard-wired output with its own driver and checks the circuit electrically (open, short to ground or voltage) – it cannot see whether the lamp lights; on CAN-based cars such faults appear as U codes. On SCR diesels a separate lamp or symbol warns of low DEF/AdBlue level, poor quality or system faults and announces speed or start restrictions (inducement). P065D reports a fault in the control circuit of this lamp. CARB requires inputs and outputs of the inducement strategy to be monitored on diesels from model years 2019–2021, and US federal rules define the inducement stages; Detroit Diesel, for example, shows the symbol below 1/8 tank and flashes it with a speed limit when empty. No manufacturer document available to us uses this code; the description follows CARB and the component. Without the lamp the driver may run into an inducement stage without warning; the code itself is not known to trigger one.

Likely causes

Symptoms

• AdBlue warning lamp does not light at ignition on, or stays on
• No early warning of low AdBlue (risk of speed limit or no-restart without notice)
• Check engine light possible (depending on the maker)

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, law.cornell.edu, static.nhtsa.gov.