P2099 Post Catalyst Fuel Trim System Too Rich (Bank 2)

P2099 is the bank 2 counterpart of P2097: the rear oxygen sensor of bank 2 keeps reporting lean exhaust, so the post-catalyst trim of that bank adds fuel until it reaches its rich-side limit. Ford sets it 5 s after the bank 2 rear bias trim reaches +0.087, with the closed loop running, coolant between 160 and 250 °F and at least 15 % fuel in the tank; GM's Bosch-based 2005 2.8 and 3.6 V6 and the 2008 3.6 LLT list it as a lean shift of the secondary trim beyond its calibrated limit, over two trips. A typical physical cause is air drawn into the exhaust ahead of the bank 2 rear sensor, at a cracked manifold, a leaking flange or a loose sensor, which makes that sensor read lean. A rear sensor that has aged lean or a front sensor reading rich gives the same result. Check fuel trims and front sensor data of both banks before replacing a sensor.

Likely causes

Symptoms

• Malfunction indicator lamp on
• Slightly higher fuel consumption

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: fordservicecontent.com, gsi.ext.gm.com, gsi.ext.gm.com.