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REMANUFACTURED INJECTORDiesel Fuel Injectors
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12-Month Warranty
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How to Test a Diesel Injector

Injector Compatibility Checker

Quick Answer

To test a diesel injector, start with a leak-off test by connecting clear hoses to the return lines and comparing fuel volumes at idle. Follow up with an electrical resistance check using a multimeter. For deeper diagnosis, use a scan tool to read injector correction values or remove the injector for a bench spray pattern test.

Symptoms Indicating Injector Failure

Engine misfire on one cylinder

A faulty injector on a single cylinder causes a rhythmic misfire noticeable at idle.

Diesel knock on cold start

Worn injectors can cause combustion knock that fades as the engine warms up.

Excessive exhaust smoke

Black smoke indicates over-fuelling, while white smoke may point to a leaking injector or poor combustion.

Poor fuel economy

A stuck-open or leaking injector wastes fuel, often reducing economy by 10–20%.

Check engine light

Fault codes P0201–P0204 or injector correction drift often triggers the MIL.

Step-by-Step Testing Methods

DIY Leak-Off Test

Easy
  1. 1Locate the injector return (spill) lines on top of the engine.
  2. 2Disconnect the return lines from each injector.
  3. 3Attach equal-length clear hoses to each injector return.
  4. 4Place the free ends of the hoses into identical containers.
  5. 5Start the engine and let it idle for 60 seconds.
  6. 6Turn off the engine and compare the fuel volumes.
  7. 7The injector with significantly more fuel is the suspect.

Tools needed: Clear hoses, containers, spanners

Multimeter Resistance Check

Easy
  1. 1Turn off the ignition and disconnect the battery.
  2. 2Unplug the electrical connector from each injector.
  3. 3Set your multimeter to the ohms (Ω) range.
  4. 4Touch the probes to the two injector connector pins.
  5. 5Record the reading and compare to the service manual spec.
  6. 6Replace any injector outside the specified range.

Tools needed: Digital multimeter

OBD-II Correction Value Check

Moderate
  1. 1Plug a compatible scan tool into the OBD-II port.
  2. 2Start the engine and let it reach operating temperature.
  3. 3Navigate to the injector correction or IMA values.
  4. 4Observe the values at idle — they should be close to 0 mg/stroke.
  5. 5Any cylinder showing ±3 mg/stroke or more needs attention.
  6. 6Cross-reference with leak-off test results to confirm.

Tools needed: OBD-II scan tool with diesel live data

Tools Required

Clear fuel-rated hose (6mm ID)
Digital multimeter
OBD-II diagnostic tooloptional
Spanner set
Rags and fuel catch tray

When Replacement Is Necessary

Replace an injector when the leak-off test shows it returning significantly more fuel than the others, the resistance reading is out of specification, correction values exceed ±4 mg/stroke, or the engine displays persistent misfires and smoke that cannot be attributed to other causes.

Compatible Injector Parts

0987654567
0987654567Bosch
£99.883450
3450Bosch
£99.903415
3415Bosch
£99.903407
3407Bosch
£99.903533
3533Bosch
£99.903467
3467Bosch
£99.903392
3392Bosch
£99.903390
3390Bosch
£99.903413
3413Bosch
£99.9045584736378
45584736378Bosch
£99.904343454321
4343454321Bosch
£99.903538
3538Bosch
£99.90

Affected Engines

N47D20 CAYC OM651 DW10C CRBC

Vehicle & Engine Combinations

AUDI A6CAYC
AUDI A6CRBC
BMW 1 SERIESN47D20

Related Fault Codes

P0201P0202P0203P0204P0300

Related Injector Problem Guides

Rough IdleBlack SmokeEngine Knock

Frequently Asked Questions

Can I do a diesel injector leak-off test at home?
Yes. All you need is clear fuel-rated hose, containers, and basic spanners. The test takes about 10 minutes and is the most effective DIY injector diagnostic.
What is a normal injector correction value?
At idle, injector correction (IMA) values should be within ±2 mg/stroke. Values beyond ±3–4 mg/stroke usually indicate injector wear.
How do I know which injector is faulty?
The leak-off test identifies the faulty injector by showing which cylinder returns the most fuel. Scan tool correction values also pinpoint the affected cylinder.

Other Testing Guides

How to Test Diesel Injectors – Complete GuideDiesel Injector Leak-Off Test – How to Diagnose a Leaking InjectorCommon Rail Injector Testing – Diagnosis & Test Procedures

Need a Replacement Injector?

All our remanufactured injectors are fully tested on a dedicated bench, calibrated to OE specifications, and supplied with a 12-month warranty.

View All InjectorsReplacement Cost Guide Call 020 3355 6581

Explore Diesel Injector Guides

Browse by VehicleBrowse by EngineInjector Part NumbersCross Reference NumbersInjector ProblemsReplacement Cost Guide

More common questions from UK installers

Specific testing, packaging and report questions our customers ask before posting injectors to us.

What does an injector test report actually show?

Every Remanufactured Injector test report shows four numbers per injector: idle delivery (mg/stroke), full-load delivery (mg/stroke), back-leakage (ml/min) and a spray-pattern grade. Anything outside OEM tolerance is flagged red. The report is a single A4 PDF emailed within 48 hours of receiving your injectors — no phone-call interpretation needed.

Do I need to send all four injectors for testing?

We recommend sending all injectors from the affected engine even if you only suspect one. Back-leakage is a relative measurement — a single injector tested in isolation cannot be compared against the others on the same engine. Testing the full set costs £80 and rules out borderline units that would otherwise come back as a workshop return weeks later.

How should I package injectors for testing?

Wrap each injector individually in bubble wrap, keep the cylinder number marked on the side (e.g. 'Cyl 3'), and place upright in a small cardboard box with packing material. Royal Mail Special Delivery or DPD Tracked is sufficient. Our address is on the confirmation email — please do not include fuel; pump the injector dry first or bag it separately.

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