OBD-II trouble code
P0612: Fuel Injector Control Module Relay Control
A fault in the relay circuit that powers the fuel injector control module — the separate high-voltage driver box that actually fires the injectors on many diesels. Lose this relay and the engine does not run rough; it stops firing altogether.
Quick facts
- System
- Powertrain
- Category
- Fuel System
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $15 – $1,300
- DIY difficulty
- Advanced DIY
What does P0612 mean?
P0612 is easy to misread, because the title compresses three different things into five words. It is not about the injectors, and it is not about the powertrain control module. It is about the relay that supplies power to a third component sitting between them.
On a large number of diesel engines — the Ford 6.0L and 6.4L Power Stroke are the platforms most owners meet this on, but the architecture appears across other diesel and some gasoline applications — the injectors cannot be driven directly by the engine control module. They need voltages and currents far beyond what a general-purpose controller's outputs can produce. So the work is handed to a dedicated fuel injector control module, a separate sealed box whose only job is to take a low-power command from the engine controller, generate the high voltage required, and switch it into the correct injector at the correct microsecond. On the 6.0L Power Stroke that module steps battery voltage up to roughly 48 volts to open hydraulically actuated injectors; other implementations differ in the numbers but not in the principle.
A module doing that kind of switching draws serious current, so it is not powered continuously. It is fed through a relay, and the engine control module commands that relay on when the engine should be able to run and off when it should not. P0612 is the report that this commanded relay circuit is not behaving: the controller energised the coil and did not see the expected result, or it saw the circuit active when it had commanded it off. The problem lives in the control side of a relay — the coil, its driver, its ground, the socket, the fuse feeding the contacts, or the wiring between them.
The consequence is what makes this code different from most fuel-system faults, and it is why the rating here is not a matter of caution. Codes like a failing injector or a drifting rail pressure sensor degrade the engine: it runs badly, it smokes, it lacks power, and you can nurse it somewhere. A fuel injector control module with no power does not degrade anything. The injectors receive no firing energy at all, so the engine either fails to start or shuts off instantly and completely. When that happens at road speed the loss is total and immediate — power steering assist and vacuum brake assist both go with it, on vehicles that are heavy and often towing. An intermittent relay fault is a stall waiting for a moment to happen in, and there is no version of this fault where continuing to drive is the sensible option.
The encouraging part is that the cheap causes are genuinely common. Relays are consumable parts with contacts that pit and coils that go open, and they are usually a few dollars in a fuse box that also holds identical spares for other systems — swapping one across is a legitimate two-minute test. Corroded or heat-damaged relay sockets are next, and they are more common than the relay itself on engines where the box sits somewhere hot. Only after those, and after confirming the controller is actually commanding the relay, does the expensive end of the list come into play.
Common causes
- Failed relay supplying power to the fuel injector control module, with pitted contacts or an open coil
- Corroded, heat-damaged or spread relay socket terminals in the underhood fuse box
- Blown fuse in the injector control module power feed
- Corroded or damaged connector at the fuel injector control module
- Chafed or broken wiring between the engine control module, the relay and the injector control module
- Poor ground for the relay coil or for the injector control module itself
- Water intrusion into the underhood fuse and relay box
- Failed fuel injector control module drawing excessive current or presenting a shorted input
- Failed relay driver inside the engine control module, or an incorrect calibration after a module replacement
Symptoms
- Engine cranks but will not start
- Engine starts and then stalls immediately
- Sudden complete stall while driving, with no roughness beforehand
- Check engine light on with P0612 stored, often alongside other injector or control module codes
- No relay click audible from the fuse box when the key is turned on
- Intermittent no-start that comes and goes with heat or vibration
- Extended cranking before the engine catches
- Loss of power steering assist and brake assist accompanying an in-motion stall
Diagnostic steps
- 1.Identify the correct relay for the fuel injector control module from the fuse box legend and the wiring diagram before testing anything. Diesel fuse boxes carry several similar relays and testing the wrong one wastes the whole diagnosis.
- 2.Swap in an identical relay from another position in the same box as a first test. It costs two minutes and resolves a meaningful share of these outright.
- 3.Listen or feel for the relay clicking as the key is turned on. No click with a known good relay fitted moves the investigation to the coil circuit, its ground, and the controller's driver.
- 4.Pull the relay and inspect the socket terminals for green corrosion, heat discolouration or spread contacts, which are more common than relay failure on engines where the box runs hot.
- 5.Measure voltage at the relay coil terminals with the key on to confirm the engine control module is actually commanding it, and check the coil ground with a voltage drop test rather than a continuity check.
- 6.Confirm the fuse feeding the relay contacts is intact and check for voltage on both sides of it under load.
- 7.Measure supply voltage arriving at the fuel injector control module connector while cranking. Voltage present there with the code still setting points away from the relay and toward the module or its ground.
- 8.Inspect the injector control module connector for corrosion and check its ground path, which on several platforms is a known trouble spot.
- 9.Check for water in the underhood fuse box before condemning any component, since a wet box explains intermittent behaviour that no single-component test will reproduce.
- 10.Confirm the engine control module calibration is correct for the vehicle if a module has recently been replaced or reflashed.
Repair cost
$15 – $1,300
A replacement relay is $10-$60 and can be fitted in minutes, which is why the swap test is always the first move. Repairing a corroded relay socket or the wiring behind it is $100-$350. Cleaning and repairing a damaged connector or ground at the injector control module is similar. A fuel injector control module itself is the expensive outcome: remanufactured units run roughly $150-$700 and new units $500-$1,100, with 0.5-2.5 hours of labour depending on where the module is mounted, and some platforms require the replacement to be programmed. Engine control module replacement, which applies only if the relay driver has failed, is $500-$1,400 including programming.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with fuel injector control module (ficm) replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.