Glow Plug Circuit (do I need a resistor?) From what I can tell from the schematic the ignition switch turns counter-clockwise to engage the glow plug circuit. When the indicator 'glows red', you then turn the key clockwise and start the engine. The glow plugs are the pencil type wired in parallel. Use manufacturer's data to identify the glow plug supply circuit. Connect a low amp clamp to PicoScope Channel A. Select the 60 A scale and zero the clamp.
P0672 Code Definition
The P0672 code is a generic powertrain code related to issues with a computer output circuit. In this case, it means that an issues has been noted with the glow plug circuit in cylinder 2 of your engine.
Codes related to the P0672 include:
- P0670: Glow Plug Module Control Circuit
- P0671: Cylinder 1 Glow Plug Circuit
- P0672: Cylinder 2 Glow Plug Circuit
- P0674: Cylinder 4 Glow Plug Circuit
- P0675: Cylinder 5 Glow Plug Circuit
- P0676: Cylinder 6 Glow Plug Circuit
- P0677: Cylinder 7 Glow Plug Circuit
- P0678: Cylinder 8 Glow Plug Circuit
- P0679: Cylinder 9 Glow Plug Circuit
- P0680: Cylinder 10 Glow Plug Circuit
- P0681: Cylinder 11 Glow Plug Circuit
- P0682: Cylinder 12 Glow Plug Circuit
What the P0672 Code Means
A glow plug is a device utilized in diesel engines to heat a cylinder head when starting up a cold engine. The diesel engine uses the high level of heat through compression, which quickly ignites the fuel. Each cylinder of the engine has a glow plug to heat the cylinder head.
When a P0672 trouble code is stored, it means that the system reference voltage allowed by the vehicle’s engine control module (ECM) has exceeded 10% of preset variance parameters.
While a glow plug will typically last 100,000 miles, they can fail before that mileage. The glow plug is installed in the cylinder head as close as possible to the cylinders combustion point. Using oil and transmission sensors, the ECM will determine if the glow plug is needed for ignition and grounds the glow plug timer module, which grounds the glow plug relay. Typically, a P0672 code means the glow plug has failed to heat up and could be damaged.
What Causes the P0672 Code?
Several problems may cause a P0672 code including:
- Damaged or defective glow plug in cylinder 2
- Damaged or defective glow plug module or timer
- Damaged or defective glow plug relay
- Blown fuse(s)
- Damaged, defective, corroded or loose wiring, harnesses, and related connectors n the glow plug circuit
What are the Symptoms of the P0672 Code?
Symptoms of a P0672 code may include:
- An illuminated warning or check engine light
- Vehicle may not start up as quickly as normal
- Vehicle may not start at all in cold weather
- Glow plug indicator light may not illuminate or illuminate longer than normal
- Additional white smoke when the vehicle starts
- Vehicle may have a loss in power
- Abnormal, loud noise from the engine
- The engine may misfire
How Does a Mechanic Diagnose the P0672 Code?
A mechanic may use several methods to diagnose a P0672 trouble code, including:
- Test glow plug timer, relay, or module
- Utilize an OBD-II scanner to check for a stored P0672 trouble code
- Check if glow plug will “warm” with battery voltage or test with digital volt/ohmmeter
- Test all system fuses to ensure they are in working order with the glow plug heater activated
- Test the glow plug after disconnecting it from cylinder 2 and check ground and resistance
- Visually inspect wiring, harnesses, and connectors related to the glow plug circuit for damage
Common Mistakes when Diagnosing the P0672 Code
If blown fuses are located, there may be an underlying problem beyond what a P0672 code holds, so it is always recommended to repair stored codes in the order in which they appear. Often, glow plug timers and relays are replaced before wiring and the glow plug itself is tested, which can lead to misdiagnosis and unnecessary repairs.
How Serious is the P0672 Code?
Because a vehicle’s safe driving operation may be impacted due to faults that store a P0672 code, this code is considered a potentially serious code. When this code appears, it is recommended to immediately take your vehicle to your local service center or mechanic for repair and diagnosis.
What Repairs can Fix the P0672 Code?
Several repairs can fix a P0672 trouble code and include:
- Replace damaged or broken glow plugfor cylinder 2
- Replace any blown fuses and repair any shorts
- Repair or replace any bent or damaged pins in electrical connectors
- Clear all codes, test-drive the vehicle, and rescan to see if any codes reappear
Additional Comments for Consideration Regarding the P0672 Code
Often, additional glow plug circuit codes will accompany a P0672, so it is recommended to do a full diagnosis and note all trouble codes that may be stored to fully repair the issue.
Need Help with a P0672 Code?
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6220.
trouble codes
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SCHEDULE P0673 DIAGNOSTIC
Get a fair and transparent estimate upfront
The purpose of this test is to examine individual glow plug operation through measurement of voltage and current.
How to perform the test
View connection guidance notes.
- Use manufacturer’s data to identify the glow plug supply circuit.
- Connect a low amp clamp to PicoScopeChannel A.
- Select the 60 A scale and zero the clamp.
- Attach the clamp around the (individual) suspect glow plug supply wire.
- Connect PicoScope Channel B voltage probe to the same glow plug supply wire.
- Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
- Start the scope to see live data.
- Switch on the ignition, wait for the glow plug warning light to extinguish, then start the engine and let it idle.
- Depending on the system type and engine operating conditions, the glow plugs may be activated for a period of time after the engine has started.
- With your waveforms on screen stop the scope.
- Turn off the engine.
- Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.
Note
The glow plugs may not activate if the ambient and engine temperature conditions are not correct.
The orientation of the clamp relative to the wire will determine whether it has a positive or negative output. If a live waveform does not appear on your screen, or appears to be inverted, try reversing the orientation of the clamp.
Example waveform
Waveform notes
These known good waveforms have the following characteristics:
Channel A
- An initial current peak of 25 A falling to 20 A over a period of approximately 2 s.
- A change to a pulse width modulated (PWM) signal with an initial peak voltage around 23 A reducing to 20 A after around 8 s.
- Zero circuit current as the engine is cranked.
- After the engine starts, a return to PWM with the peak current stabilising at around 20 A.
- Continued PWM operation for a further 1 min 30 s, to give a total on time of approximately 1 min 45 s.
Channel B shows the voltage driving the current in the glow plug circuit:
- With the engine off, the supply voltage is at 10.8 V (battery voltage).
- Once the engine is running the circuit supply voltage is the system voltage, at around 13.5 V.
- When the supply voltage is removed, no current flows through the circuit.
Waveform Library
Go to the drop-down menu bar in the lower left corner of the Waveform Library window and select glow plug current or glow plug voltage.
Further guidance
Glow plugs support diesel fuel combustion and emissions control processes.
Injected diesel fuel ignites if the cylinder charge temperature reaches 850° C during compression. However, this temperature may not be achieved with cold ambient air conditions and engine components. In these circumstances, the glow plugs are activated to heat the cylinder charge and ensure adequate combustion.
Different types of glow plug are available, with rapid glow systems replacing the traditional direct current type. The later systems tend to use ceramic glow plugs, reducing the glow wait time by more than 50%. Their operating temperatures are in the range from 1000° to 1100° C. Manufacturer specifications vary but these systems are not activated with ambient temperatures above 9°C or if the vehicle is driven and engine speed exceeds 2500 rpm.
Rapid glow plugs have two coils internally connected in series, a small heating coil at the plug tip and a larger regulating coil within the plug case. These systems use Pulse Width Modulation (PWM) of the supply voltage to regulate the circuit current and to control glow plug temperature.
Rapid glow systems operate in several modes:
Pre-heat: increases the temperature of the cylinder charge within the combustion chamber prior to start up. As soon as the glow plug temperature has stabilised after their initial activation, they will be switched via PWM to prevent overheating.
Engine cranking: the glow plugs are deactivated to ensure maximum battery capacity is available for the starter motor.
Post heat: the glow plug temperature is regulated via PWM whilst the engine is running. This helps to reduce engine cold running noise and emissions. The post heat run time can vary greatly as it depends on a variety of environmental factors, the engine conditions, and the system design.
Warning: it is often impossible to distinguish standard and rapid glow type glow plugs by visual inspection. Many of the latter systems operate at lower voltages, such as 4 to 5 V or 7 V. Therefore, glow plugs must not be tested using a directly applied voltage, such as that from the battery positive terminal, a test probe or other test device. An unregulated current through the glow plug will cause irreversible damage.
Glow plug circuits are susceptible to a variety of faults, such as:
- Short or open circuits or high resistances within the circuitry or connections
- Control failures, such as ECM, control module or relay failures
- Application of 12 V directly onto a glow plug outside of ECM control (incorrect testing)
- Thermal failures, such as those caused by:
- excessive carbon build-up (causing overheating)
- an incorrect injector spray pattern (over cooling)
- incorrect timing and/or fuel delivery
The most common glow plug fault is a thermal failure from overheating.
Symptoms of failed glow plugs:
- Malfunction Indicator Lamp (MIL) or glow plug warning lamp illumination
- Diagnostic Trouble Codes (DTCs)
- Engine non-starting
- Excessive emissions when cold
- Excessive cranking time
- Rough running when cold
- Excessive particulate build-up in the Diesel Particulate Filter (DPF), Exhaust Gas Recirculation (EGR), Selective Catalytic Reduction (SCR) and intake (via EGR) systems
Diagnostic trouble codes
Selection of component-related Diagnostic Trouble Codes (DTCs):
P037D
P037E
P037F
P0380
P0381
P0382
P0383
P0384
P064C
P066A
P066B
P066C
P066D
P066E
P066F
P0670
P0671
P0672
P0673
P0674
P0675
P0676
P0677
P0678
P0679
P067A
P067B
P067C
P067D
P067E
P067F
P0680
P0681
P0682
P0683
P0684
P068C
P068D
P068E
P068F
P069A
P069B
P069C
P069D
P06B9
P06BA
P06BB
P06BC
P06BD
P06BE
P06BF
P06C0
P06C1
P06C2
P06C3
P06C5
P06C6
P06C7
P06C8
P06C9
P06CA
P06CB
P06CC
P06CD
P06CE
P06CF
P06D0
U0106
U0307
U0407
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Disclaimer Suitable accessories
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