P2149 Fuel Injector Group B Supply Voltage Circuit/Open — Causes & Fix
Updated for 2026 diagnostics & repair guidance
P2149 at a Glance
What it means
The ECU has detected a voltage fault in the supply circuit for fuel injector group B (typically cylinders 3 and 4 on a 4-cylinder, or cylinders 4–6 on a 6-cylinder).
Most common cause
Damaged wiring harness, corroded connectors, or failed injector(s) in group B.
Severity
Serious — affected cylinders will not fire correctly.
Can you drive?
Short distances only. The engine will run rough on fewer cylinders.
Typical repair cost
£40–£350 depending on wiring vs. injector replacement.
What Does P2149 Mean?
P2149 indicates the ECU has detected an open circuit or voltage fault in the power supply to fuel injector group B. Modern diesel ECUs group injectors into banks (Group A and Group B) for power management. When the supply voltage to group B is lost or abnormal, the ECU cannot fire those injectors properly, causing the engine to run on half its cylinders.
Common Causes
Injector-Related Causes
Failed injector(s) in group B
A short-circuit inside an injector solenoid can pull down the entire group's supply voltage, triggering P2149.
Other Possible Causes
Damaged injector wiring harness
Heat, vibration, or rodent damage to the wiring between the ECU and injector group B. Common in the engine bay near exhaust components.
Corroded injector connectors
Water ingress into injector connectors causes high resistance or open circuits in the group B supply.
ECU power driver failure
The transistor bank in the ECU that powers group B injectors has failed. Less common but requires ECU repair.
Aftermarket wiring modification
Poorly executed repairs or aftermarket installations can damage the injector supply circuit.
Symptoms Drivers Notice
- Engine running on half cylinders (very rough idle)
- Severe vibration through the vehicle
- Major loss of power
- Engine management light illuminated (often flashing)
- Black smoke from exhaust
- Engine may stall at idle
- DPF warning light due to incomplete combustion
Vehicles Commonly Affected
Can You Still Drive with P2149?
Driving should be limited to reaching a workshop. The engine is running on approximately half its cylinders, which means severe vibration, minimal power, and rapid DPF contamination. A flashing engine light with P2149 means stop driving immediately.
How Mechanics Diagnose P2149
- 1
Read and confirm fault codes
Confirm P2149 and check for companion codes (P2146 for group A, or individual cylinder codes P0201–P0208).
- 2
Inspect wiring harness to group B injectors
Visually check the wiring from ECU to the affected injector bank for damage, chafing, or burns.
- 3
Measure supply voltage at injector connectors
With ignition on, check for 12V supply at each group B injector connector. No voltage confirms a wiring or ECU fault.
- 4
Test individual injector resistance
Disconnect each group B injector and measure solenoid resistance. A short-circuit (near 0 ohms) identifies a failed injector pulling down the group.
- 5
Isolate and swap test
Disconnect each group B injector one at a time. If removing one restores voltage to the others, that injector has an internal short.
Repair Solutions & Costs
Repair or replace wiring harness
If wiring damage is found, repair the affected section with proper soldering and heat-shrink. Full harness replacement for severe damage.
Replace failed injector(s)
If an injector has an internal short-circuit, replacement is the only fix. Remanufactured injectors are a cost-effective, OEM-spec option.
Clean or replace connectors
Corroded connectors can be cleaned with electrical contact cleaner or replaced if severely damaged.
ECU repair
If the ECU power driver has failed, specialist ECU repair or replacement is needed.
When Injector Replacement Is Required
Injector replacement is needed when an individual injector's solenoid resistance is out of spec (typically <0.1 ohms indicates a short circuit). The failed injector pulls down the entire group B supply voltage.
Compatible Injector Part Numbers
5 injectors compatible with engines affected by P2149.
Cross Reference Numbers
OEM and alternative part numbers for injectors affected by P2149.
Affected Vehicle & Engine Combinations
Need a Replacement Injector?
UK-tested remanufactured injectors with 12-month warranty. Search by engine code or vehicle registration.
Need it fast? Same-day dispatch on in-stock injectors.
Order before 2pm for next working day delivery (UK mainland). Call us on 020 3355 6581.
Engine-Specific Guides
Frequently Asked Questions
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Need Help With P2149?
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