OBD-II trouble code
U0105: Lost Communication with Fuel Injector Control Module
The network has lost the module that actually drives the injectors. This module is unlike any other node on the bus because it handles serious voltage and current of its own — which is why a communication code here points at the module's power supply far more often than at the network.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $120 – $1,600
- DIY difficulty
- Shop recommended
What does U0105 mean?
Most fuel systems switch injectors directly from the engine computer, but some cannot. Hydraulically actuated diesel injectors need tens of volts to open. Solenoid injectors on a high-pressure system need a large initial current pulse followed by a precisely controlled holding current. Piezo injectors need a shaped high-voltage waveform timed to the microsecond. Those jobs are given to a dedicated injector driver module, which takes timing and quantity commands from the engine computer over the network and generates the actual drive waveform itself. U0105 is set when that module stops answering.
The reason this code deserves a different approach from the other lost-communication codes is that this module is not a low-power participant on the bus. Almost every other node on a vehicle network draws a modest current to run a processor and a transceiver. This one contains a power supply that steps voltage up, and switching stages that dump substantial current into inductive loads thousands of times a minute. It has its own heavy fused feed and its own dedicated ground for that reason. So when it drops off the network, the probability weighting is different from a body or comfort module: a supply that has degraded, a ground that has developed resistance, or an internal power section that has failed is a more likely explanation than a bus wire, and it should be tested before the network is.
That gives a specific and unusually productive first measurement. Many of these modules report their own internal supply voltage as a live data parameter, and where they do, the reading under three conditions — key on, cranking, and idle — is far more informative than any resistance check. A supply that is adequate at idle but collapses during cranking is the classic signature of an aging internal power section, and it explains a fault that presents as an intermittent no-start with a healthy battery. Where the module cannot report that value, measuring the voltage at its main feed with the engine cranking gets at the same question.
Heat is the other structural fact. This module is normally mounted in the engine bay, often on the engine itself, because its drive wiring has to reach the injectors and stay short. It therefore lives with underhood temperature, engine vibration, and in some installations a fair amount of oil mist. Internal solder joint fatigue in the power stages is a recognised failure mode in exactly those conditions, and it produces a fault that is heat-dependent — present when hot, gone when cold — which is worth confirming before condemning wiring on the strength of a test done on a cold engine.
The consequence for the driver is immediate and total rather than gradual. Without this module there is no injector drive at all, so the engine does not run rough or lose power; it stops, or it never starts. There is nothing to nurse home.
One planning note matters before any part is ordered. Where injectors are individually characterised at manufacture, their calibration values live in this module rather than in the engine computer. Fitting a replacement without transferring or re-entering those values gives an engine that runs, but runs unevenly, with knock or misfire complaints that look like an entirely new fault. Confirm how the calibration data is handled on the specific application before the old module is removed.
Common causes
- Degraded internal power supply in the module, most visible as a voltage that collapses during cranking
- High-resistance or corroded dedicated ground for the module's power stages
- Blown high-current fuse feeding the module, distinct from the small ignition feed
- Internal solder joint fatigue in the power section from underhood heat and vibration
- Oil or coolant intrusion into the module or its connector at an engine-mounted location
- Damaged bus wiring or connector terminals at the module
- Heat-related failure that is present when hot and absent when cold
- Low or unstable system voltage from a weak battery, which this module tolerates less than most
- Another fault on the same network segment taking down more than one node
Symptoms
- Engine cranks normally but does not start, with no fuel being injected at all
- Sudden stall with no warning and no preceding roughness
- No-start that occurs only when the engine is hot, or only when it is cold
- Check engine light with injector circuit or fuel system codes stored alongside
- Scan tool reaches other modules normally but cannot reach the injector driver
- Module-reported supply voltage reading low or dropping during cranking
- Fault that first appeared after work on the engine or its wiring
- Rough or uneven running immediately after a replacement module was fitted
Diagnostic steps
- 1.Test the module's power and ground before the network. This node draws far more current than an ordinary bus module, so its supply is the more likely failure and it is quicker to check.
- 2.Read the module's reported internal supply voltage in live data if the platform provides it, and take the reading key on, while cranking, and at idle. A value that is acceptable at idle and collapses during cranking indicates a failing internal supply.
- 3.Where no live value exists, measure at the module's main feed with the engine cranking rather than at rest. A supply problem that only appears under load is invisible in a static test.
- 4.Perform a loaded voltage-drop test on the module's dedicated ground. Resistance that measures fine on a meter can be significant once the power stages are drawing current.
- 5.Check the high-current fuse for this module specifically. It is separate from the small ignition feed and is easy to overlook.
- 6.Establish whether the fault is temperature-dependent. Note whether it appears hot or cold, and repeat the test in the condition where the fault is present rather than the one where it is convenient.
- 7.Inspect the module and its connector for oil misting and fluid intrusion, which is a real risk at engine-mounted locations and is visible without tools.
- 8.Only after supply, ground and temperature have been addressed, measure the bus wires at the module connector and confirm continuity back to the network.
- 9.Before ordering a module, find out how injector calibration data is handled on this application, since values that live in the module have to be transferred or re-entered or the engine will run unevenly on a good part.
Repair cost
$120 – $1,600
A fuse or a ground repair is $100 to $300 once found, and on this module a ground repair is a more likely outcome than on an ordinary network node because of the current it carries. Diagnosis is $150 to $350. Connector and wiring repair is $200 to $600. Module replacement is $450 to $1,300 including programming, and the figure runs higher on diesel applications where the module is engine-mounted and access is poor. Budget separately for injector calibration data where the application stores it in this module — omitting that step produces an engine that runs badly on a new part and is the most common way this repair has to be revisited.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with control module replacement & programming preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.