P2146 Injector Group A Supply Voltage — Causes & Fix
Updated for 2026 diagnostics & repair guidance
P2146 at a Glance
What it means
The ECU has detected a supply voltage fault affecting injector group A (typically cylinders 1 and 4).
Most common cause
ECU injector driver failure, main relay fault, or wiring short.
Severity
Serious — can affect two cylinders simultaneously.
Can you drive?
Not recommended. Two cylinders may be disabled.
Typical repair cost
£200-£500 for ECU repair; £100-£350 per injector if required.
What Does P2146 Mean?
P2146 is a manufacturer-specific code indicating the ECU has detected a voltage fault in the power supply to injector group A. On most diesel engines, injectors are grouped in pairs — group A typically covers cylinders 1 and 4. This code usually indicates an internal ECU fault rather than an injector problem, but injector short circuits can trigger it.
Common Causes
Injector-Related Causes
Injector short circuit
A short circuit inside one injector can overload the ECU driver, triggering P2146 and potentially damaging the ECU.
Other Possible Causes
ECU injector driver failure
The internal power transistor that drives injector group A has failed. This is the most common cause and requires specialist ECU repair.
Main relay or power supply fault
The relay providing power to the injector circuit has failed or has high resistance.
Wiring harness short
A short circuit in the injector wiring harness, often caused by chafing against the engine block.
Water ingress to ECU
Water entering the ECU housing can cause internal corrosion and driver failure.
Symptoms Drivers Notice
- Engine runs very rough or only on two cylinders
- Significant loss of power
- Engine management light on (often flashing)
- Engine may not start or stall immediately after starting
- Excessive smoke from exhaust
- Vehicle may enter limp mode
Vehicles Commonly Affected
Can You Still Drive with P2146?
Not recommended. P2146 often disables two cylinders simultaneously, making the vehicle unsafe to drive. If the engine management light is flashing, stop driving immediately and arrange recovery.
How Mechanics Diagnose P2146
- 1
Read all stored fault codes
P2146 often accompanies P0201/P0204. The combination helps identify whether it is an ECU or injector problem.
- 2
Check injector resistance
Measure each injector in group A. A short-circuited injector (very low resistance) can trigger P2146.
- 3
Test supply voltage at injectors
With ignition on, measure voltage at the injector connector. Should be battery voltage (12-14V).
- 4
Check main relay
Test the injector supply relay for correct operation and contact resistance.
- 5
ECU driver test
Using manufacturer diagnostic software, command each injector individually. If group A does not respond, ECU driver failure is confirmed.
Repair Solutions & Costs
ECU repair (specialist)
Specialist ECU repair to replace the failed injector driver transistor. Most cost-effective option.
ECU replacement
Full ECU replacement. Required if the ECU is beyond repair. Must be coded to the vehicle.
Replace short-circuited injector
If an injector short circuit caused the P2146, replace the faulty injector AND have the ECU checked.
Repair wiring
Repair any short circuits found in the injector wiring harness.
When Injector Replacement Is Required
Injector replacement is required when an injector short circuit triggered the P2146. After replacing the injector, the ECU must also be tested — a short-circuited injector may have damaged the ECU driver.
Compatible Injector Part Numbers
5 injectors compatible with engines affected by P2146.
Cross Reference Numbers
OEM and alternative part numbers for injectors affected by P2146.
Affected Vehicle & Engine Combinations
Need a Replacement Injector?
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Engine-Specific Guides
Frequently Asked Questions
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