Code 45 or rich exhaust is most likely caused by one of the following:

Check for fuel contaminated oil.
If an open occurs on circuit No. B2, HEI induced electrical noise may result, causing simulated reference pulses to be picked up by ECM. Additional pulses result in a higher than actual engine speed signal. The ECM will increase injector pulse width to match fuel requirements of increased RPM signal. Tachometer will show higher than actual RPM, which can help in diagnosing this problem.
Check charcoal canister for fuel saturation. If full of fuel, check canister control and hoses.
An output causing ECM to sense a lower than normal vacuum can cause system to go rich. Disconnecting MAP sensor allows ECM to set a fixed value for the sensor. If rich condition is gone with MAP sensor disconnected, replace sensor.
An intermittent TPS output causes system to go rich due to a false acceleration indication.
Inspect oxygen sensor for silicone contamination from fuel, or use of improper RTV sealant. Sensor may have a White powdery coating and result in a high but false signal voltage (rich exhaust). ECM will reduce amount of fuel delivered to engine, causing a severe surge driveability problem.
Check for EGR valve sticking open at idle, usually accompanied by a rough idle or stall complaint, especially at idle.

For intermittent inspection, see INTERMITTENTS in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Fig 1: Code 45 Schematic - O2 Sensor (Rich Fuel Mixture)

Courtesy of ISUZU MOTOR CO.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Diagnostic Aids