P0612

Fuel Injector Control Module Relay Control

P0612 is a generic OBD-II powertrain diagnostic trouble code: Fuel Injector Control Module Relay Control. It is logged by the engine control unit when the fuel/inj monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0612
Group
Powertrain
System
Fuel/Inj
Severity
Critical (limp mode / no-start)
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What P0612 means

P0612 is a generic powertrain code meaning the engine control module has found a fault in the part of itself that controls the fuel injector control module relay. Some engines, particularly diesels and other designs with high-current or high-voltage injector drivers, do not switch the injectors directly from the ECU. Instead a separate fuel injector control module handles the injector drive, and that module gets its power through a relay commanded by the ECU. P0612 is the ECU reporting that its own relay control output or the internal circuit that monitors it is not behaving as expected.

The ECU commands the relay on and then checks the feedback from that output. If the commanded state and the sensed state do not agree, for example the relay is commanded on but the output remains inactive, or the driver reports an over-current or fault condition, the ECU stores P0612. Because the code is defined as an internal control module fault it usually sits alongside a self-check of the ECU driver stage, so it can be set either by the driver circuit itself or by external conditions on that circuit that make the self-check fail.

The practical consequence is that the injector control module may lose its power supply. If the relay never closes, the injectors get no drive at all, which produces a crank-no-start. If the fault is intermittent, the engine can stall or misfire unpredictably, so P0612 is treated as a serious code even though it points inside the ECU.

Common causes

Most-frequently reported root causes when P0612 is logged.

  • 1
    A failed or worn injector control module relay whose contacts or coil no longer respond correctly.
  • 2
    A blown fuse or an open power feed on the relay or injector control module supply circuit.
  • 3
    Corroded or water-damaged relay socket, fuse box terminals, or harness connectors on that circuit.
  • 4
    Damaged, chafed, or shorted wiring between the ECU, the relay, and the injector control module.
  • 5
    Poor ground connections for the ECU or the injector control module producing false feedback readings.
  • 6
    Low or unstable system voltage from a weak battery, bad cables, or a failing charging system.
  • 7
    A failed injector control module drawing abnormal current through the relay circuit.
  • 8
    A genuine internal ECU driver or monitoring circuit failure, which should be the last conclusion.

Symptoms drivers notice

The check engine light is on, sometimes with additional warnings on the dash.
The engine cranks but will not start, or starts and immediately dies.
Long or hard starting, especially when cold or after the vehicle has sat.
Rough running, misfires, or stalling while driving as the relay circuit drops in and out.
Noticeably poor acceleration and rough or unstable idle.
Multiple other engine codes appear at once because the injector control module is losing power.

How to diagnose P0612

A typical diagnostic flow when this code is present.

  1. 1
    Read all stored codes and freeze-frame data first, and note any companion injector, relay, or low-voltage codes.
  2. 2
    Test the battery and charging system, since low or unstable voltage can cause false internal module faults.
  3. 3
    Inspect the relevant fuses, the relay and its socket, and the connectors at the ECU and the injector control module for corrosion, water, and heat damage.
  4. 4
    Command the relay with a scan tool if the vehicle supports it and confirm whether it actually clicks and passes power downstream.
  5. 5
    Check for voltage drop and clean grounds on the ECU and injector control module power and ground circuits under load, not just key-on.
  6. 6
    Check continuity and the absence of shorts on the relay control wire between the ECU and the relay along its full length.
  7. 7
    Only after wiring, grounds, fuses, relay, and supply voltage all test good should the injector control module or the ECU be evaluated using the manufacturer procedure, including any applicable software updates.

Related powertrain codes

Frequently asked questions

Can I keep driving with P0612?

No, this one should not be ignored. The circuit powers the module that drives the injectors, so the engine can stall or fail to restart without warning. If the vehicle is still running, get it to a workshop directly rather than continuing to use it normally.

Why won't my engine start with this code?

If the relay never closes, the fuel injector control module receives no power and cannot fire the injectors. The engine cranks normally because the starter is unaffected, but with no injection there is no combustion, so you get a crank-no-start.

Does P0612 mean I need a new ECU?

Not necessarily. The definition points inside the ECU, but a failed relay, blown fuse, corroded socket, damaged wiring, bad ground, or low battery voltage can all make the ECU's internal check fail. Those are cheaper and far more common, and should be tested first.

Is this expensive to fix?

It depends entirely on the cause. A relay, fuse, or corroded socket is inexpensive. Harness repair costs mainly diagnostic labour. Replacing an injector control module or the ECU is the expensive end, and those normally need programming to the vehicle to work at all.

Disabling P0612 in software

RaceTune can permanently disable P0612 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECU families we can disable P0612 on

We hold the DaVinci A2L disable definitions for these families, so the exact P0612 path and mask addresses are mapped. verified marks a confirmed disable definition. We support many more — upload your file and our identifier will match it automatically.

  • Bosch MD1CP002 verified
  • Bosch MD1CS001 verified

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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