What are the common causes of P066A?

A failed cylinder 1 glow plug drawing low current. An open or chafed wire in the cylinder 1 glow plug circuit. Corrosion or water in the glow plug connector. A weak battery pulling glow voltage low. A failed glow plug control module.

Measure glow plug resistance at cylinder 1 and compare to the others. Test the cylinder 1 glow plug feed wire for opens and shorts. Inspect the glow plug connector for corrosion or water. Check battery voltage during the glow cycle. Replace the cylinder 1 glow plug if resistance is out of range. Clear the code and retest.

P066A

Cylinder 1 Glow Plug Control Circuit Low

System: Computer output circuits (P code)
Lamp: Check Engine Light
Category: Powertrain - Computer and Auxiliary Controls

What it means

P066A means Cylinder 1 Glow Plug Control Circuit Low.

Check these first

A failed cylinder 1 glow plug drawing low current
An open or chafed wire in the cylinder 1 glow plug circuit
Corrosion or water in the glow plug connector
A weak battery pulling glow voltage low
A failed glow plug control module

What to do next

Measure glow plug resistance at cylinder 1 and compare to the others
Test the cylinder 1 glow plug feed wire for opens and shorts
Inspect the glow plug connector for corrosion or water
Check battery voltage during the glow cycle
Replace the cylinder 1 glow plug if resistance is out of range
Clear the code and retest

Look up another code

Code or symptom

Enter a full code or a symptom. Press / to search. How to read a code

Type a code above, or start from a symptom or a common code.

Updated

Generic SAE J2012 definition. Last updated 2026-10-10.