P2099

Code

MITSUBISHI P — Powertrain

Post catalyst system too rich 2

Brand: MITSUBISHI

Type: P — Powertrain

Views: UK: 17 EN: 24 RU: 21

AI status

Completed

ready

Completed 100%

Page language: EN

Faulty downstream (post-catalyst) O2 sensor (Bank 2)
Wiring or connector problems to the downstream O2 sensor
Leaking or stuck-open fuel injector(s) on Bank 2
High fuel pressure or faulty fuel pressure regulator
Contaminated or failing catalytic converter on Bank 2
Faulty upstream O2 sensor or MAF/airflow sensor giving incorrect fueling commands

Read and record freeze-frame and live data with a scan tool (focus on upstream and downstream O2 sensors, short/long-term fuel trims, and fuel trims for Bank 2)
Compare upstream (sensor 1) and downstream (sensor 2) O2 sensor behavior and voltages on Bank 2
Check for pending or related codes (fuel trim, injector, fuel pressure, catalytic efficiency)
Inspect wiring and connector for Bank 2 downstream O2 sensor (corrosion, damage, poor ground)
Perform fuel pressure test at idle and under load
Inspect injectors on Bank 2 for leakage or dripping (fuel smell/capture test)

Bank 2 downstream O2 sensor voltage: typically 0.1–0.9 V (rich > ~0.6–0.7 V, lean < ~0.2–0.3 V)
Post-catalyst sensor should show a more stable/flattened signal than upstream sensor; rapid switching like upstream can indicate catalyst inefficiency
Short-term fuel trim (STFT) and long-term fuel trim (LTFT) for Bank 2: significant negative trims (large negative %s) can indicate commanded leaning while downstream reads rich, or large positive trims indicate overall rich condition
Fuel rail pressure: consult model-specific spec (commonly 3–5 bar key-on idle; refer to service manual)
Upstream O2 (Bank 2 sensor 1) should switch frequently under closed-loop; downstream (sensor 2) should be steady or show attenuated switching if catalyst is functioning

Retrieve codes and freeze-frame data; note operating conditions when code set (temp, load, engine speed).
Using scan tool, monitor Bank 2 upstream (sensor 1) and downstream (sensor 2) O2 voltages and fuel trims during warm idle and steady cruise. Compare behavior between sensors.
Visually inspect downstream O2 sensor connector and wiring for damage, corrosion, or poor ground. Repair as necessary and clear code to retest.
Test downstream O2 sensor: measure voltage and response; if sensor reads high (rich) or is slow/unresponsive compared with upstream, consider replacement.
Check fuel system: measure fuel pressure at rail during idle and under load; compare to factory spec. Inspect for leaking injectors on Bank 2 (fuel smell, drip tests, or remove rail and pressurize for leak-down).
Inspect for intake/exhaust leaks upstream of the downstream sensor that could skew readings; repair leaks and retest.
Verify upstream sensor and MAF/airflow sensor operation. A faulty upstream sensor or MAF can cause incorrect fueling and downstream rich condition.
If sensors, wiring and fuel delivery check good but problem persists, evaluate catalytic converter efficiency (temperature differential pre/post cat, backpressure test, or lab emissions test). A degraded catalyst can cause abnormal downstream readings.
After repairs, clear codes and perform a verified drive cycle to ensure code does not return. If intermittent, perform extended road test and re-scan.

⚠️ Status

Post-catalyst oxygen sensor (Bank 2) indicates rich condition — system reports post-catalyst too rich (P2099).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours

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P2099 — Post catalyst system too rich 2