System Too Rich at Idle (Bank 1)

What it means

The ECU has had to remove much more fuel than normal on bank 1 at idle and has reached its limit. "Rich" means too much fuel or too little air. A rich mixture wastes fuel and can damage the catalytic converter.

Symptoms

• Check engine light on
• Poor fuel economy
• Black smoke or strong fuel smell from the exhaust
• Rough idle
• Fouled spark plugs

Probable causes

Most likely first

1. 1Leaking or stuck-open fuel injector
2. 2Fuel pressure too high (faulty regulator or blocked return line)
3. 3EVAP purge valve stuck open
4. 4Faulty coolant temperature sensor reading cold
5. 5Dirty or failing MAF sensor over-reading airflow
6. 6Clogged air filter
7. 7Oil contaminated with fuel

How to diagnose it

Work through these in order before buying parts

1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
2. 2Check fuel trims for bank 1. Negative trims confirm the ECU is pulling fuel.
3. 3Check coolant temperature on live data. A sensor that reads cold makes the ECU add fuel.
4. 4Disconnect and plug the EVAP purge line at idle. If trims return to normal, the purge valve is stuck open.
5. 5Test fuel pressure, and check that it holds steady after the engine is shut off (a drop points to a leaking injector).
6. 6Smell the engine oil; a strong fuel smell suggests leaking injectors.
7. 7Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

• Replace leaking injectors
• Replace the fuel pressure regulator
• Replace the EVAP purge valve
• Replace the coolant temperature sensor
• Clean or replace the MAF sensor
• Replace the air filter