P21FF: Fuel Control System B Too Rich at Higher Load (Bank 2)

P21FF closes the series: bank 2's second fuel path is rich in the upper load range although its correction already removes the largest reduction allowed. No manufacturer publishes criteria for it. Under CARB, a fuel system fault must be stored once adaptive control has exhausted the range the maker allows; threshold, load window and the number of trips are left to the manufacturer. On a V engine with dual injection, port injectors on bank 2 that over-deliver at long pulse widths, or excessive pressure in the shared low-pressure rail, would push this bank rich. If only bank 2 is affected, also compare the bank 2 front sensor signal with bank 1. Drivers rarely feel anything, but consumption rises. P2194 is the system A twin, P21FD the bank 1 code.

Bank 2 is the side without cylinder 1, so it only exists on V or boxer engines.

Symptoms

• Check engine lamp on
• Increased fuel consumption

Most likely causes

• Port injectors on bank 2 over-delivering at long pulse widths
• Bank 2 front oxygen sensor reading rich
• Excessive pressure in the shared low-pressure rail

What to check, in order

Start with the simplest. You can tick off each step.

1. Check short-term and long-term fuel trims in live data
2. Look for air leaks at hoses and gaskets
3. Check the mass air flow sensor (MAF) and, if appropriate, clean it with a dedicated cleaner
4. Measure the fuel pressure
5. Check the injectors and the oxygen sensor

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P21FF means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 1: Air and fuel
• FF: Specific fault in that system

Frequently asked questions

Can I keep driving with code P21FF?

You can drive in moderation for a short time. A very lean or very rich mixture can damage the engine or the catalytic converter.

What causes code P21FF?

The most common causes are: port injectors on bank 2 over-delivering at long pulse widths; bank 2 front oxygen sensor reading rich; excessive pressure in the shared low-pressure rail.

Related codes

• P21FEFuel Control System B Too Lean at Higher Load (Bank 2)
• P21FDFuel Control System B Too Rich at Higher Load (Bank 1)
• P21F7Fuel Control System B Too Rich Off Idle (Bank 2)
• P21FBFuel Control System B Too Rich at Idle (Bank 2)
• P2194System Too Rich at Higher Load (Bank 2)
• P2BF3Fuel Control System B Too Rich Bank 2

Sources

• law.cornell.edu: 13 CCR 1968.2
• patents.google.com: en
• fordservicecontent.com: OBD Operations Summary Gasoline 2020 2023

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.