Code
P0159
MITSUBISHI
P — Powertrain
Oxygen sensor2(rear) response
Views:
UK: 26
EN: 33
RU: 32
AI status
Completed
Completed
100%
Causes
- Faulty downstream (Bank 2, Sensor 2) oxygen sensor
- Damaged/corroded wiring or connector to the sensor
- Heater circuit failure in the oxygen sensor (if heated)
- Exhaust leak upstream of the sensor or at the sensor flange
- Degraded or clogged catalytic converter reducing sensor signal change
- Contaminated sensor (oil, coolant, silicone, fuel additives)
Symptoms
- Check Engine Light / MIL illuminated (P0159 stored)
- Failed emissions or readiness monitor for catalytic system (Bank 2)
- Possible reduced fuel trim/catalyst monitoring accuracy (may not affect drivability)
- Poor or inconsistent long-term fuel trim or failed emissions test
What to check
- Read freeze frame and full DTC history with a scan tool; note engine temperature, load, RPM when code set
- Inspect wiring and connector for Bank 2 Sensor 2 for damage, corrosion, pin push-out, or water intrusion
- Use a scan tool to monitor live O2 sensor voltages (Bank 1 & Bank 2, Sensor 1 & Sensor 2) at operating temperature
- Compare upstream (Sensor 1) and downstream (Sensor 2) voltages for Bank 2
- Perform a wiggle test on harness/connectors while monitoring live data for signal interruption or change
- Check for exhaust leaks upstream of the downstream sensor and at flange connections
Signal parameters
- Typical narrowband O2 voltage: ~0.1–0.9 V (switching behavior for upstream sensor)
- Downstream (Sensor 2) expected: relatively steady compared with upstream; should still show some voltage changes when catalyst efficiency changes
- Heater circuit resistance (if equipped): typically a few ohms to a few tens of ohms (manufacturer-specific)
- Response time: downstream sensor should respond within a few hundred milliseconds to changes; slow response indicated when signal change is abnormally delayed or sluggish
Diagnostic algorithm
- Confirm code and note freeze frame; check for other related codes (upstream O2, heater, catalyst)
- Visually inspect sensor wiring and connector at Bank 2 Sensor 2; repair any obvious damage or corrosion
- With engine at normal operating temperature, use a scan tool to observe live voltages on Bank 2 Sensor 1 and Sensor 2; verify Sensor 1 is switching and Sensor 2 shows expected downstream behavior
- Perform heater circuit check: disconnect sensor, measure heater resistance and check for supply voltage/ground while key on/engine start (if sensor is heated)
- If wiring and heater are good, perform a wiggle test on harness while monitoring sensor output to find intermittent faults
- Check for exhaust leaks upstream of the sensor and repair if present; retest after repair
- Compare downstream sensor behavior bank-to-bank; if Bank 2 Sensor 2 is sluggish but Bank 1 Sensor 2 is normal, consider replacing the sensor
- If swapping sensors (from bank to bank) is practical and safe, observe if the code follows the sensor to confirm sensor failure versus wiring/catalyst issue
- Inspect catalytic converter (temperature probe or infrared thermometer) before and after cat while engine under load — small temp difference or low efficiency may indicate catalyst problem
- After repairs or component replacement, clear codes and perform a drive cycle/road test to confirm P0159 does not return and readiness monitors complete
Likely causes
- Wiring harness damage or poor connector connection to Bank 2 Sensor 2
- Failed heater element inside the downstream O2 sensor
- Contaminated or aged downstream O2 sensor
- Exhaust leak or restricted/inefficient catalytic converter causing muted downstream signal
Fault status
Status
P0159 — Oxygen sensor (Bank 2, Sensor 2) slow/late response detected. Indicates downstream O2 sensor signal change is outside expected timing/voltage parameters; inspect sensor, wiring/heater, exhaust, and catalytic converter.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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