P0682 OBD-II Trouble Code: Cylinder 12 Glow Plug Circuit

P0682 code definition

A P0682 trouble code indicates a problem in the glow plug circuit in cylinder 12. Other glow plug-related trouble codes that might be stored along with this code include a: P0670, P0671, P0672, P0673, P0674, P0675, P0676, P0677, P0678, P0679, P0680, P0681, P0683, and P0684 code.

What the P0682 code means

When the Powertrain Control Module (PCM) detects a variance in the reference voltage coming from the cylinder 12 glow plug circuit, a P0682 trouble code is stored and the Check Engine Light illuminates. This variance in the reference voltage must exceed the manufacturer's recommendations by at least 10 percent to trigger the storage of the trouble code.

What causes the P0682 code?

Some common causes of a P0682 trouble code include:

• Shorted, corroded, or loose wiring or connectors within the glow plug circuit
• Faulty glow plugs, glow plug relays, timer, or modules
• Blown fuses

When seeking to diagnose and fix trouble codes, the mechanic should make sure to repair trouble codes in the order they are stored on the PCM.

What are the symptoms of the P0682 code?

Some of the symptoms encountered with a P0682 trouble code include trouble starting the engine, an increase in the amount of white smoke emitting from the exhaust pipe, engine misfires, excessive engine noise while starting, and the glow plug indicator staying on longer than it should.

How does a mechanic diagnose the P0682 code?

Properly diagnosing and repairing a P0682 trouble code requires the use of an advanced scanner and a digital volt/ohmmeter on the part of the mechanic. Using the tools gathered, the mechanic should next perform the following steps:

• Inspect any related wiring, connectors, and components for damage, corrosion, or fault

• After replacing the wiring, connectors, and components, clear the code and test the system to see if the code comes back. This includes a test drive by the mechanic

• If upon examination the wiring, connectors, and components seem to be in good condition, hook the scanner to the diagnostic connectors and download both the freeze frame data and any stored codes for further diagnosing

• Check the connector of the faulty glow plug with the digital volt/ohmmeter while the glow plug heater lamp is on. The mechanic is making sure there is a reference voltage and ground signal present at the connector

• The mechanic should also check the resistance value of any potentially faulty glow plugs before replacing them using the volt/ohmmeter. Compare any findings to the manufacturer's specifications

• If voltage is not present at the connector, the mechanic should also test the fuses to see if any are blown

• The mechanic should also test the glow plug relay, timer, and module for fault, comparing any findings to the manufacturer's specifications

• If all wiring, connectors, and components appear and test as normal, disconnect and test the PCM using the digital volt/ohmmeter to determine the resistance of the circuit

• Clear the trouble code and re-test the glow plug system to see if the code returns

Common mistakes when diagnosing the P0682 code

Some mechanics make the mistake of not testing the system fully and replace glow plug timers and relays even though they are not faulty. This, in turn, leads to a misdiagnosis and results in the trouble code returning.

How serious is the P0682 code?

The biggest concern with this trouble code is getting the engine to start properly. A diesel engine ignites fuel through the aid of the glow plugs, which heat the cylinder chamber prior to firing. When this heat is not present, the vehicle can have problems starting, especially during cold weather. When a problem is encountered with the glow plug system, the vehicle also runs less efficiently and loses unburnt fuel via the exhaust, as evidenced by the increase in white smoke.

What repairs can fix the P0682 code?

To repair a P0682 trouble code, the mechanic should perform the following:

• Replace any defective wiring, connectors, or components
• Replace the glow plug connector if it is faulty
• Replace any bad glow plugs
• Replace the glow plug timer, relay, or module if they test as faulty
• Replace the PCM if it tests as faulty. This requires the mechanic to reprogram the PCM
• Replace any blown fuses. The mechanic should also determine what is causing the fuses to blow and fix that problem as well

Need help with a P0682 code?

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