By iCarsoft Official Store Technical Team, Automotive Diagnostics Editors · Updated September 7, 2026 · OEM technical references checked
Quick Answer
The P0671 code means cylinder 1 glow plug circuit/open. It does not prove that the cylinder 1 glow plug alone has failed. Save the scan, identify the exact architecture, and test the physical and electrical paths before selecting a repair.
What Does the P0671 Code Mean?
P0671 is standardized as Cylinder 1 Glow Plug Circuit/Open. It names a monitored result, not a guaranteed failed part. The reporting module, suffix and companion faults determine the relevant test branch.
P0671 concerns the cylinder 1 glow-plug current path during the enabled monitor. Ford's open-load monitor and Audi's low-current example distinguish this circuit/open fault from high- or low-control classifications.
Cylinder numbering must come from the engine identification, not from a photograph of another diesel. Glow plugs can also differ in construction and operating requirements. A replacement that physically fits is not automatically electrically correct. Preserve the plug part number and check the manufacturer application before testing or installation.
The Audi Q7 reference book lists P0671 as a cylinder 1 glow-plug circuit fault. Ford's diesel monitoring summary distinguishes an open-load fault from a short-to-battery fault. These examples explain the classification; their current limits and test conditions apply only to the specified engines.
Record which channels were commanded and which measurements were actually available. A missing current PID should be marked unavailable in the report, not converted to a zero-current failure. If battery or module supply was unstable, repeat the approved test after correcting that prerequisite before comparing one cylinder with the others.
Separate P0671 from adjacent fault families
| Code | General description | Key distinction |
|---|---|---|
| P0672 | Cylinder 2 glow plug circuit/open | Different cylinder channel. |
| P0380 | Glow plug/heater circuit A | Broader system classification. |
| P0683 | Glow module to PCM communication | Investigate communication and shared support. |
| P2609 | Intake air heater system performance | Separate intake-heating system. |
Record the complete P0671 description. The suffix, reporting module and companion faults can change the diagnostic path. Current manufacturer evidence governs when the queue wording conflicts.
P0671 Symptoms and Likely Causes
P0671 symptoms depend on fault status and the fallback strategy. Record what the driver and modules reported. A symptom list is not a parts list.
Compare the first cold start with warm restarting and record battery condition.
Combustion may be uneven while the cylinder warms; this does not exclude injector or compression faults.
Record duration and temperature; persistent dense smoke requires diagnosis beyond this code.
A warm start does not exercise every preheat monitor.
Practical cause-checking order
- Connection evidence: A disconnected or weak terminal can interrupt cylinder 1 current without an internally failed plug.
- Electrical path: Open or resistive output wiring can imitate an open plug; isolate the harness before testing.
- Supporting condition: Weak shared supply or module grounding deserves priority when several glow channels fail together.
- Component evidence: A plug with an internally open heater is one possible result of the specified channel test.
- Final decision branch: An individual output driver is considered only after its load, wiring, module supply and command are proved.
Did P0671 appear after recent glow-plug, harness or battery service? Recheck disturbed connectors, grounds, hoses, fluids, part numbers and setup steps for the cylinder 1 glow-plug current path. Record battery and software history; a post-repair code does not prove the new part is defective.
How Serious Is P0671, and Can You Drive?
Arrange diagnosis promptly. When the warning is steady, operation remains normal and the owner's manual permits it, a short light-load trip to a repair facility may be reasonable. Avoid demanding use until the cylinder 1 glow-plug current path is understood. P0671 does not provide a universally safe distance.
Record temperature, load, speed, start state and recent service. Do not reproduce a severe symptom on public roads; another warning can make the situation more urgent.
Stop and arrange a tow if dense smoke, severe misfire, electrical burning or unsafe running persists.
Glow plugs and circuits get hot and carry high current. Do not apply battery voltage directly to an unknown low-voltage or pressure-sensing plug. Stop for persistent heavy smoke or severe misfire.
How to Diagnose P0671 in the Right Order
-
Preserve the cold-start and glow-channel record
Save cold-start temperature, battery condition, preheat command and other glow-channel/module faults. Keep the original status and operating conditions so the next test answers the failure that actually occurred. If the event is intermittent, record what changes before reconnecting parts or cycling power.
-
Identify cylinder 1 and verify shared prerequisites
Confirm OEM cylinder numbering and the plug type and voltage rating before locating channel 1. If several channels fail, test shared module feeds, grounds and supply stability before individual plugs. For an isolated channel 1 fault, follow its plug, harness and driver branch. Confirm the exact connector view, equipment version and test state before measuring.
-
Inspect the cylinder 1 connector and harness
Inspect the cylinder1 connector and output harness for disconnection, corrosion, heat damage or poor terminal retention. Check the suspected area without disturbing unrelated components. Photograph damage, note which circuits share a connection, and retest after a controlled correction so cause and effect remain traceable.
-
Compare supported commanded-current evidence
Compare supported channel-current evidence with other channels under the prescribed command; missing scan data is not zero current. Use the approved adapters and test instrument for the circuit. An unloaded continuity result can miss a fault that appears only during operation; an unsupported scan parameter is unavailable evidence, not a zero reading.
-
Test the isolated plug and its circuit
With the system isolated by OEM procedure, test the plug and harness separately using the specified low-resistance/current method, accounting for test-lead resistance. Compare evidence from the controller with the appropriate independent physical test. A request or learned label does not establish that the connected system can perform its function under the failed conditions.
-
Verify the repaired channel and a proper cold start
After repairing the proven fault, repeat the approved glow-channel test and verify the next proper cold start under the required conditions. Record the cylinder 1 command and response, check for returning faults, and confirm the original failure has been resolved. Do not call a cleared warning a verified repair before the glow monitor has run.
Specifications are vehicle-specific. There is no universal voltage, resistance, current, pressure, waveform, timing, temperature, percentage, learned value or drive cycle for P0671. Test state, connector location and system design change what a valid value means. Use only specifications for the exact VIN and do not transfer the OEM example in this article to another application.
P0671 Repairs and Typical Costs
The correct P0671 repair follows the failed test. Wiring, a physical repair, a proven component, software and controller work are different outcomes. Do not replace an assembly from the generic code alone.
After installation, recheck connector seating, harness clearance, fluid or mechanical setup and every required learn. When several channel codes appear together, compare their occurrence times before ordering a full set of plugs. A shared module supply problem can affect multiple outputs, while one isolated failure may stay local to its plug or harness. Neither pattern by itself is proof; it determines the next controlled test.
| Possible path | Current US estimate |
|---|---|
| Diagnosis and confirmation of cylinder 1 glow-plug current path | VIN-specific quote |
| Verified connector, harness or supporting-system repair | VIN-specific quote |
| A component replacement supported by the failed test | VIN-specific quote |
| Required OEM setup and repeat-condition verification | VIN-specific quote |
There is no single national P0671 repair price because these rows are alternative outcomes. Ask for an itemized estimate showing diagnostic time, parts, labor, fluids, service-information access and verification. Location, taxes, related damage and warranty eligibility change the total. Do not add the rows together or authorize an assembly without the supporting failed test.
Using iCarsoft CR Eagle P for P0671
On a supported vehicle, iCarsoft CR Eagle P can retrieve accessible module faults, save available freeze frame, display ECU-provided live data and create a diagnostic report. For P0671, preserve the original evidence and compare related modules before clearing an erasable record.
Preserve the cylinder 1 glow-plug current path evidence
iCarsoft CR Eagle P
Review supported codes and relevant live data together. Confirm the exact VIN, controller access, PIDs and any requested active test with iCarsoft before purchase; generic product capabilities do not guarantee a P0671-specific function.
Check current CR Eagle P price and availabilityCheck CR Eagle P compatibility by VINThe official product page describes full-system diagnostics, available freeze frame and live data, and supported bidirectional tests and ECU coding; availability varies with the vehicle, ECU and software. Active-test and coding availability varies by vehicle and ECU and requires VIN confirmation. Follow OEM prerequisites and stop for abnormal operation.
Know the measurement boundary. The scanner reports information supplied by the vehicle. It does not directly prove terminal tension, circuit load capacity, leakage, pressure, temperature, mechanical travel or internal condition in the cylinder 1 glow-plug current path. It also cannot replace the specified low-resistance meter, current clamp and approved probes when the OEM procedure requires them. Interpret commanded and reported values alongside measured evidence.
Verify the P0671 Repair
After repair, verify connectors, harness clearance, setup and controller supply. Save post-repair findings, then clear only erasable records through the approved procedure. Battery disconnection is not a repair.
Run the manufacturer's applicable verification conditions in a safe workshop or route. Compare the original operating state with current data for the cylinder 1 glow-plug current path, and check current and pending faults in related modules. One clean start or idle period does not prove that every conditional monitor has completed.
If P0671 returns, compare its suffix, status, failure order and operating conditions with the saved baseline before replacing another part. Revisit the failed branch and inspect anything disturbed. Keep mechanical repair, monitor completion, readiness and local inspection eligibility as separate outcomes.
A permanent P0671 can remain immediately after a successful repair. If the vehicle stores it as a permanent DTC, a scan tool or battery disconnect cannot erase it. Once current and pending faults are absent, the OBD system removes the permanent record only after the applicable monitor reruns and passes.
Related Cylinder 1 Glow-Plug Current Path Code Guides
P0671 Frequently Asked Questions
Does P0671 mean the named component is bad?
No. P0671 describes cylinder 1 glow plug circuit/open, not a confirmed part. It also does not prove that the cylinder 1 glow plug alone has failed. Test accessible wiring, supplies, grounds and supporting physical conditions, then follow the exact monitor tree. Replace a component only when its branch fails or an applicable OEM action specifically supports it.
What should I check first for P0671?
Save every module's codes and freeze frame before clearing. Confirm the full definition, suffix and VIN architecture. Then inspect recent glow-plug, harness or battery service, connectors and shared supplies. Those facts determine whether the next test needs the specified low-resistance meter, current clamp and approved probes or a manufacturer-specific functional procedure.
Can I drive with the P0671 code?
Only consider a short light-load trip when operation is normal and the owner's manual permits it. Stop if dense smoke, severe misfire, electrical burning or unsafe running persists. The code number cannot establish a safe mileage allowance, and another warning can make the situation more urgent.
Why did P0671 return after a part was replaced?
P0671 can return after a plug replacement if the cylinder 1 connector, harness, driver or shared supply still fails, or if the replacement plug has the wrong specification. Recheck the recorded failure conditions and test the correct isolated circuit. Account for lead resistance during low-resistance measurements, and use the prescribed commanded-current test when required. A passive resistance reading alone does not replace that test.
What should a P0671 repair estimate include?
A VIN-specific estimate is required because diagnosis may lead to wiring, a supporting physical repair, a verified component, software or a controller. Ask which failed test supports the quote and whether diagnosis, taxes, setup and post-repair verification are included.
Can CR Eagle P diagnose and clear P0671?
On a supported vehicle, CR Eagle P can organize available faults, freeze frame, live data and reports, and can clear erasable records after repair. Confirm exact ECU coverage. It cannot force-clear a permanent DTC or replace physical measurements for the cylinder 1 glow-plug current path.
The iCarsoft Official Store Technical Team maintains the store's fault-code library. This guide organizes published manufacturer evidence and verified product information; it does not document a hands-on test of a particular vehicle or claim an individual engineer's review.
Technical and cost references
- 2014 Audi Q7 Quick Reference Specification Book. Audi lists the cylinder 1 glow-plug circuit/open fault on printed page 154. The monitor criteria apply to the specified engine.
- Ford 2012 MY OBD System Operation Summary for Diesel Engines. Ford distinguishes glow-system open-load and short-to-battery checks. Use the relevant engine procedure rather than transferring test limits.
- Ford 2014 OBD-II 5 Digit Code Interpretation. Ford code terminology cross-check; this catalog does not establish that every listed code occurs on one model.
- California Bureau of Automotive Repair — On-Board Diagnostic Test Reference. Permanent DTCs are removed by the vehicle after applicable verification, not by a scan-tool erase command.
Product information: Official iCarsoft CR Eagle P page.
Editorial note: General diagnostic education, not a substitute for the owner's manual, current VIN-specific service information or professional inspection. Test limits, procedures, coverage and costs vary. Related articles provide context; apply only the specifications and repair procedures that match the vehicle. No universal failure rate, repair price or outcome is implied.
