The P0673 is an issue with the electrical circuit of the glow plug in cylinder 3. Glow plugs are essential for diesel engines, providing the necessary heat to start the engine in cold conditions. When there’s a problem with the circuit, such as a fault in the wiring, the glow plug itself, or the control module, it can lead to starting issues or reduced engine performance. Addressing this problem promptly is crucial to maintaining the engine’s reliability, especially in colder weather.
P0673 quick overview
| Meaning | P0673 – Cylinder 3 Glow Plug Circuit |
| Is it serious? | Yes, it can impact engine start-up and performance, especially in cold weather. |
| Possible causes | – Faulty glow plug in cylinder 3 – Issues with the glow plug harness or connector – Problems with the glow plug control module – Wiring problems, such as shorts or opens in the circuit |
| How to diagnose? | Inspect the glow plug in cylinder 3 for damage or wear. Check the wiring and connectors for damage, corrosion, or poor connections. Test the glow plug harness for continuity and resistance. Verify the operation of the glow plug control module. Use a multimeter to check for proper voltage at the glow plug. |
P0673 Meaning
When you encounter a P0673 code, it means there’s a snag in the system that helps your diesel engine start in cold weather. Each cylinder has its own glow plug, and cylinder 3’s isn’t communicating correctly with the engine’s computer. This could be because the glow plug is worn out, there’s a problem in the wiring, or the module that controls the plug isn’t working right. If this plug can’t do its job, you might find your engine hard to start on chilly mornings, or it might not run as smoothly. To fix it, mechanics will often start by checking the glow plug itself for any signs of trouble, then move on to the wiring and connections to make sure everything’s in good shape.
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How to fix P0673 – learn from mechanics
I looked into P0673 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Volkswagen
Vehicle Information 2002 Volkswagen Jetta TDI 1.9L
Issue + Repair History
- Car came from another shop with glow plug codes for cylinders 1 and 3.
- Checked glow plugs, which showed a 7.5 amp current when on.
- Replaced glow plug relay and glow plugs.
- Visually inspected old glow plug harness but found no visible issues.
- Changed the glow plug harness based on suggestions.
Other OBD2 Codes + Test Results
- p0671: Glow plug 1
- p0673: Glow plug 3
Mechanic Suggestions
- Consider replacing the glow plug harness with an updated kit, as Volkswagen often has harness replacement kits.
- Check for internal corrosion or discoloration in the glow plug wiring harness.
- Verify the resistance of all glow plugs.
- Note that on some VW TDI engines, the DTC numbers are reversed for the cylinders.
- Test glow plugs using a wire connected to the battery positive terminal, as VW diesel engine glow plugs are numbered backward.
- Keep in mind that even small differences in resistance in the individual glow plugs can trigger a code due to the sensitive programming of the ECM.
Final Fix
- Replaced the glow plug harness, despite not finding any obvious issues upon visual inspection.
- Issue resolved, and no more glow plug codes detected.
Case #2: GMC
Vehicle Information 2006 GMC Sierra 2500 HD SLT 6.6L
Issue + Repair History
- Vehicle came in with several codes and reduced engine power.
- Codes included: p0652 (5V reference low voltage), p0522 (EOP low voltage), p0405 (EGR low voltage), p0462 (fuel level low voltage), p0672, p0673, p0674, p0677 (glow plug circuit).
- Found no 5V reference coming out of ECM except on oil pressure sensor.
- Replaced ECM with OEM unit, programmed it, but issue persisted.
Other OBD2 Codes + Test Results
- p0652: 5 volt reference low voltage
- p0522: Engine oil pressure low voltage
- p0405: EGR low voltage
- p0462: Fuel level sensor low voltage
- p0672: Glow plug control circuit
- p0673: Glow plug circuit
Mechanic Suggestions
- Check for shorted sensors pulling down voltage.
- Test all 5V reference circuits, even those not listed under codes.
- Verify vehicle voltage problem, including battery and charging system.
- Check terminal pin tension at ECM for poor connections.
- After snipping the wire far enough away from the PCM, use an ohm meter to check for continuity to ground and start chasing down the short.
- Plug in sensors one at a time and observe voltage to identify the faulted sensor.
- Inspect C108 and C107 connectors for pushed out pins.
Final Fix
- Discovered smashed wires behind power steering bracket where someone had replaced water pump.
- Repaired wires, restoring proper functionality.
- Issue resolved, no more reduced engine power or codes.
Case #3: Dodge
Vehicle Information 2008 Dodge Sprinter 2500 3.0L
Issue + Repair History
- Initially came in with the MIL and glow plug light on, with a code P0672 for cylinder 2 glow plug open circuit.
- Replaced cylinder 2 glow plug, then subsequent visits revealed failures in other cylinders, ultimately leading to replacement of all glow plugs and the glow plug module.
- Despite the replacements, the issue persisted, with all 6 glow plugs failing internally again.
Other OBD2 Codes + Test Results
- P0671: Cylinder 1 glow plug open circuit
- P0672: Cylinder 2 glow plug open circuit
- P0673: Cylinder 3 glow plug open circuit
- P0674: Cylinder 4 glow plug open circuit
- P0675: Cylinder 5 glow plug open circuit
- P0676: Cylinder 6 glow plug open circuit
Mechanic Suggestions
- Check the glow plug module ground (G109) near the left fender area. Load test the ground at the module connector.
- Load test all the glow plug circuits, including the ground. Ensure the power source is good.
- Measure the total current going through all the glow plugs to see if they are staying on longer than they should. Check how the controller turns the glow plugs on; a short to ground in the harness could cause them to stay on and burn up.
- Put a current clamp around each glow plug and check the draw.
Final Fix
- Changed all 6 glow plugs again after further inconclusive testing.
- Load tested the ground circuit with no voltage drop.
- Load tested the power feed and inspected for any possible shorts in the harness, but found nothing conclusive.
- Assumed that something is intermittently keeping the glow plugs on longer than they should or they are turning on when not needed.
- It is possible, the glow plug relay was causing the fault
- System was fine after the replacements, but the issue might resurface.
How to diagnose P0673
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Explanation |
|---|---|
| Inspect the glow plug in cylinder 3 | Check for physical damage or signs of malfunction; replace if necessary. |
| Check wiring and connectors | Look for damaged, corroded, or loose connections that could interrupt the circuit. |
| Test the glow plug harness | Ensure continuity and proper resistance, indicating no breaks or shorts in the wiring. |
| Verify glow plug control module operation | Confirm that the module is functioning correctly and sending the correct signals. |
| Measure voltage at the glow plug | Use a multimeter to ensure the glow plug is receiving the correct voltage for operation. |
In these cases, solutions ranged from replacing the glow plug harness to addressing issues with smashed wires or faulty control modules. Such fixes highlight the importance of thorough diagnostics to accurately identify and rectify the root cause of the P0673 code, ensuring optimal engine performance and reliability, especially in conditions requiring efficient glow plug operation.
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko