P066B - OBD Trouble Code

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What does P066B code relate to? Why are glow plugs used and where are they used? They are used in diesel engine for preheating the cylinder before the engine starts. If the glow plug of cylinder 1 is not opening correctly, P066B code will be set by the engine control module PCM.

To initiate the piston movement, the diesel engines use high compression instead of spark. As there is no spark, you have to increase cylinder temperature in order to maximize compression. In order to increase this, glow plugs are used in each cylinder. In each cylinder, a glow plug is threaded into the cylinder head. Through the glow plug timer, battery voltage is applied. If the voltage is correctly applied, it will shine bright red and help to increase the cylinder temperature. Once the level is reached, control unit blocks the voltage till it reaches normal state.

What causes this problem with the Cylinder 1 Glow Plug Control Circuit High?

• Corrupt glow plug/s.
• Opening or short in the glow plug control circuit.
• Loose or faulty glow plug connector.
• Defective glow plug timer.

1. Power Control Module - Is your PCM damaged or broken? Looking for the right replacement part? Parts Avatar has the replacement part for every make and model.
2. Engine Control Module - If the ECM malfunctions, it disturbs the entire system. Fix the issue to avoid further troubles.
3. Glow Plug - A faulty/corrupt or bad plugs will not shine bright red. They have to be immediately replaced or fixed.
4. Glow Plug Relay - Check if the glow plug relay functions normally. If not, there can be an opening in the circuit which needs to be fixed.
5. Glow Plug Control Module - A corrupt or damaged glow plug control module needs replacement to avoid P066B error code.
6. Glow plug wiring harness - Are there any oil leaks in the wiring joints? they have to be cleaned immediately.

Willing to know some common symptoms of OBD Code P066B? Your wish is our demand. Have a look at them below:

Common Symptoms

• Too much black smoke from exhaust.
• Engine issues.
• Late engine starts up.
• Less fuel efficiency.
• Codes related to engine misfire may be stored.

To correct this issue, you might need to undergo few replacements for the defective parts such as:

• Replacing the glow plug

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Here are some steps which you should follow in order to diagnose this fault code:

• To perform proper diagnosis, a diagnostic scanner, vehicle information, and a DVOM will be required. Use the DVOM and find the TSB. A TSB will help you to arrive at a proper diagnosis that has information of vehicle make, model and year of manufacturing.
• Further to diagnose correctly you will need diagnostic flowcharts, wire diagrams, connector face views, connector pinout charts, component positions, and testing procedures.
• Once you inspect the glow plug and its wires, connect the scanner to the diagnostic port and recover all the stored codes and freeze frame data. Test drive to see if the code is reset. The PCM will enter readiness mode or the code will be reset. If either of these 2 happens, continue diagnosing. If not, there is irregular connection and the condition has to be made worse.
• Best idea is to remove glow plugs and apply battery voltage. If it glows bright, condition is good, if not, test it with DVOM and you will see that it does not meet manufacturer’s specification. Be careful when performing the test.
• Use the scanner to start the timer and test for voltage at the glow plug connector. If there is no voltage, test the power supply for the timer and controller. Also, check the fuses, relays, when the circuit is loaded. If the fuse is loaded it will appear to function and lead to wrong path.
• If all fuses and relays function properly, there can be an open or shorted circuit which can be simply replaced.
• A defective glow plug alone cannot cause a P066B circuit. Sometimes a variation in the circuit will also give rise to this error code.
• Make sure you diagnose the right cylinder before proceeding.

Common Mistakes When Diagnosing the P066B Code

• Faulty glow plug control module.
• Damaged glow plug.
• Faulty glow plug relay.
• Damaged glow plug relay harness.