P2BB2: Alternative Fuel Tank Empty

What it means

The AFCM detects that the alternative fuel tank is empty. Bi-fuel vehicles may switch to gasoline operation; mono-fuel vehicles cannot continue without refuel.

At a glance

• Usually lights the check-engine light

How it works

The alternative-fuel control module estimates the amount of fuel remaining using the tank-level signal and its fuel-use information. P2BB2 sets when that system determines the alternative-fuel tank is empty; the cause may be an actually depleted tank or a level signal that falsely reports empty.

Common causes

Most likely first.

1. Tank actually empty - refuel required
2. Level sensor reads empty incorrectly

Symptoms

• Alternative-fuel warning light or low-fuel message
• Switch to the primary fuel, if equipped
• Engine stops or will not start, if no usable fuel remains

How to diagnose it

1. Check the alternative-fuel gauge or message and confirm whether the vehicle has recently been refuelled.
2. Review scan-tool fuel-level data and related tank-sender codes to see whether the reported level agrees with the display.
3. If the tank may be empty, refuel it using the correct fuel and the vehicle's prescribed procedure.
4. If the tank is known to contain fuel, inspect the level-sensor connector and wiring for damage or poor contact.
5. Test the tank-level sensor and its circuit against the manufacturer's service information.

Common fixes

• Refill the alternative-fuel tank if it is empty.
• Reconnect or repair a loose or damaged level-sensor connector or wiring.
• Replace a level sensor that fails its test.
• Correct a confirmed fuel-level calibration issue.

Can I keep driving?

A bi-fuel vehicle may continue on its primary fuel if that system is available, but a mono-fuel vehicle can stall or fail to start when the alternative-fuel tank is empty. Refuel promptly and do not assume a displayed empty level is false if the vehicle is losing power.