Glow plugs - current

The purpose of this test is to evaluate the condition of the glow plugs based on the total current draw, while also confirming their operation time.

How to perform the test

View connection guidance notes.

  1. Connect the high amp current clamp to PicoScope channel A, switch on and zero the clamp.
  2. Place the current clamp onto a battery (+) cable, or directly onto the glow plug supply cable from the control relay (access permitting).
  3. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  4. Start the scope to see live data.
  5. Switch on the ignition to activate the glow plugs. Wait a few seconds before starting the engine.
  6. Allow the engine to idle and observe your waveform. After a short period, it is usual for the glow plugs to be switched off.
  7. Stop the engine and turn off the ignition.
  8. Stop the scope.
  9. Use the Waveform Buffer, Zoom and Measuring tools to examine your waveform.

 Note; the orientation of the current 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

This known good waveform has the following characteristics:

A current spike up to around 100 A when the glow plugs are switched on, followed by an immediate decrease to around 70 A, and then a more gradual decrease to about 45 A over the next 5 s.

The current remains stable at 45 A until the glow plug relay is switched off.

The total on time is just over 11 s.

Waveform Library

Go to the drop down menu in the lower left corner of the Waveform Library window and select, Glow Plug Current.

Example glow plug

Further guidance

The function of glow plugs is to support diesel fuel combustion and related emissions control processes.

Injected diesel fuel will ignite if the cylinder charge temperature reaches 850° C during compression. However, with cold ambient temperatures, intake air and engine components, this may not be achieved. In these circumstances glow plugs are used to heat the cylinder charge and aid combustion.

Glow plugs are designed to operate within temperatures from 850° to 1100° C. They are controlled either via a relay switched by the Engine Control Module (ECM) or by a dedicated glow plug control unit/timer.

Use appropriate vehicle data to identify the system switching and on time characteristics.

Glow plugs also heat the cylinder charge to support the operation of diesel particulate filter (DPF) systems: a DPF requires very high exhaust temperatures during passive and active (either running or forced) regeneration processes. Any fault in the glow plug system will prevent regeneration and will inevitably lead to the excessive build-up of particulates in the filter and eventual blockage.

One of the main causes of glow plug failure is overheating, as such their control systems use Pulse Width Modulation (PWM) to constantly regulate their temperature when they operate during engine running conditions.

It is important to be able to identify control failures, such as those that might occur in the ECM, glow control module, or other relays, as a cause of glow plug failure.

Other causes of glow plug failure can be;

  • Improper injector spray pattern.
  • Incorrect engine timing.
  • Application of 12 V directly onto a glow plug outside of ECM control; some systems operate at 6 V (incorrect testing).

Characteristics of failed glow plugs;

  • Engine will not start.
  • Excessive cranking time.
  • Rough running when cold.
  • Excessive emissions when cold.
  • Particulate build up in diesel particulate and other exhaust gas treatment systems (including EGR valves and SCR systems).

The expected glow plug supply circuit current can be determined from wattage rating of the glow plugs, which is available in appropriate technical literature.

Dividing the combined power consumption of the glow plugs by the circuit operating voltage gives the circuit current:

For example, in a 12 V, 4-cylinder diesel engine with 150 W glow plugs, the current is calculated as follows:

Combined power consumption = 4 x 150 W = 600 W;

System voltage = 12 V;

Current = Power / Voltage;

Therefore, the steady-state circuit current will be around 50 A.

Diagnostic trouble codes

Selection of component related Diagnostic Trouble Codes (DTCs):

P037D Glow plug sensing circuit

P037E Glow plug sensing circuit low

P037F Glow plug sensing circuit high

P0380 Glow plug/heater circuit A

P0381 Glow plug/heater indicator circuit

P0382 Glow plug/heater circuit B

P0383 Glow plug control module control circuit low

P0384 Glow plug control module control circuit high

P064C Glow plug control module

P066A Cylinder 1 glow plug control circuit low

P066B Cylinder 1 glow plug control circuit high

P066C Cylinder 2 glow plug control circuit low

P066D Cylinder 2 glow plug control circuit high

P066E Cylinder 3 glow plug control circuit low

P066F Cylinder 3 glow plug control circuit high

P0670 Glow plug module control circuit

P0671 Cylinder 1 glow plug circuit

P0672 Cylinder 2 glow plug circuit

P0673 Cylinder 3 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

P067A Cylinder 4 glow plug control circuit low

P067B Cylinder 4 glow plug control circuit high

P067C Cylinder 5 glow plug control circuit low

P067D Cylinder 5 glow plug control circuit high

P067E Cylinder 6 glow plug control circuit low

P067F Cylinder 6 glow plug control circuit high

P0680 Cylinder 10 glow plug circuit

P0681 Cylinder 11 glow plug circuit

P0682 Cylinder 12 glow plug circuit

P0683 Glow plug control module to PCM communication circuit

P0684 Glow plug control module to PCM communication circuit range/performance

P068C Cylinder 7 glow plug control circuit low

P068D Cylinder 7 glow plug control circuit high

P068E Cylinder 8 glow plug control circuit low

P068F Cylinder 8 glow plug control circuit high

P069A Cylinder 9 glow plug control circuit low

P069B Cylinder 9 glow plug control circuit high

P069C Cylinder 10 glow plug control circuit low

P069D Cylinder 10 glow plug control circuit high

P06B9 Cylinder 1 glow plug circuit range/performance

P06BA Cylinder 2 glow plug circuit range/performance

P06BB Cylinder 3 glow plug circuit range/performance

P06BC Cylinder 4 glow plug circuit range/performance

P06BD Cylinder 5 glow plug circuit range/performance

P06BE Cylinder 6 glow plug circuit range/performance

P06BF Cylinder 7 glow plug circuit range/performance

P06C0 Cylinder 8 glow plug circuit range/performance

P06C1 Cylinder 9 glow plug circuit range/performance

P06C2 Cylinder 10 glow plug circuit range/performance

P06C3 Cylinder 11 glow plug circuit range/performance

P06C4 Cylinder 12 glow plug circuit range/performance

P06C5 Cylinder 1 glow plug incorrect

P06C6 Cylinder 2 glow plug incorrect

P06C7 Cylinder 3 glow plug incorrect

P06C8 Cylinder 4 glow plug incorrect

P06C9 Cylinder 5 glow plug incorrect

P06CA Cylinder 6 glow plug incorrect

P06CB Cylinder 7 glow plug incorrect

P06CC Cylinder 8 glow plug incorrect

P06CD Cylinder 9 glow plug incorrect

P06CE Cylinder 10 glow plug incorrect

P06CF Cylinder 11 glow plug incorrect

P06D0 Cylinder 12 glow plug incorrect

U0106 - Lost Communication with Glow Plug Control Module.

U0307 - Software Incompatibility with Glow Plug Control Module.

U0407 - Invalid Data Received from Glow Plug Control Module.

GT006-6

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • 200 A / 2000 A (high amps) DC current clamp

    £259.00

  • 600 A DC (high amps) current clamp

    £139.00

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Guided test: Glow plugs - current