Ignition Retard Request Circuit Fault
The engine computer is having trouble communicating with the ignition timing retard system, like a dimmer switch that won't respond to commands. This prevents the engine from properly adjusting spark timing when needed for emission control.
The ECM sends voltage signals to the ignition retard solenoid to delay spark timing during specific operating conditions. It monitors the circuit for proper voltage delivery, signal response, and continuity. A fault occurs when the ECM detects open circuits, shorts, or voltage readings outside expected ranges.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Solenoid Control Voltage | 11-14V when commanded | Below 8V or above 15V, or no response |
| Circuit Resistance | 4-8 ohms | Open (infinite) or shorted (below 1 ohm) |
Code P1782 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P1782 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.