Engine

P039E — Cylinder 1 Combustion Performance Fault

Severity: medium Drive with care, to a shop

What P039E means

The engine control module monitors crankshaft speed and other signals, and it has found that cylinder 1 is burning fuel less effectively than the others. Normally the injector delivers fuel, the spark plug ignites it at the right moment, and every cylinder contributes equal power. The code points to cylinder 1 but does not say which part has failed.

Symptoms

  • Check Engine Light on
  • Rough idle or shaking
  • Misfires or stumbling
  • Reduced power and sluggish acceleration
  • Increased fuel consumption
  • Hesitation when accelerating

Possible causes

  1. Worn or faulty spark plug in cylinder 1
  2. Failed ignition coil or damaged coil wiring
  3. Clogged or faulty fuel injector on cylinder 1
  4. Low compression in cylinder 1 (valves, rings, piston, head gasket)
  5. Vacuum leak near cylinder 1 intake runner
  6. Fuel delivery problem such as low fuel pressure

How to diagnose

  1. Scan all codes and freeze-frame data, and look for related misfire codes such as P0301
  2. Inspect the cylinder 1 spark plug for wear, fouling, oil and gap
  3. Swap the cylinder 1 coil with a neighboring one and see if the problem follows
  4. Inspect connectors and wiring for the coil and injector for corrosion or damage
  5. Test the injector: resistance, operation, balance and spray pattern
  6. Check for intake vacuum leaks with a smoke machine or by inspecting hoses and gaskets
  7. Run a compression or leak-down test on cylinder 1
  8. Check fuel pressure

Common fixes

  • Replace spark plugs, at least the one in cylinder 1
  • Replace the cylinder 1 ignition coil
  • Clean or replace the fuel injector
  • Repair vacuum leaks and replace damaged hoses or gaskets
  • Repair the engine mechanically (valves, piston, rings, head) if compression is low

Questions and answers

What does P039E mean?

The ECM detected incomplete or unstable combustion in cylinder 1. Common causes are a bad spark plug, coil, injector, vacuum leak or an internal engine problem.

Can I drive with P039E?

Only briefly and gently if the engine runs smoothly. If the check engine light flashes, stop, because misfires can damage the catalytic converter.

How can I tell if it is the coil or the spark plug?

Swap the cylinder 1 coil with another cylinder's coil, clear the code and retest. If the fault moves with the coil, replace it. If it stays on cylinder 1, check the plug, injector and compression.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.