P0135
The heater in the upstream oxygen sensor on bank 1 isn't working as the computer expects
Severity: MonitorOxygen sensors codes
Oxygen sensors measure leftover oxygen in the exhaust. The upstream sensor (sensor 1, before the catalytic converter) is used to correct the fuel mixture; the downstream sensor (sensor 2, after the converter) is mainly used to check the converter. Each sensor has a heater so it works soon after a cold start.
How these codes differ
- Heater codes (P0135, P0141, P0031, P0037) are about the sensor's built-in heater circuit, not its oxygen reading. Sensor 1 is upstream and sensor 2 is downstream, so P0135 and P0031 point to the bank 1 upstream sensor's heater and P0141 and P0037 to the bank 1 downstream sensor's heater. P0031 and P0037 specifically report the heater control circuit reading low.
- P0137 (low voltage) and P0138 (high voltage) are about the bank 1 downstream sensor's actual reading. A reading stuck low or high can be the sensor, but it can also be a real lean or rich exhaust or an exhaust leak near the sensor, so check fuel trim before replacing the sensor.
- Downstream sensor faults matter for the catalyst test: the computer judges the converter by comparing upstream and downstream sensors, so a faulty downstream sensor can make catalyst results unreliable.
Codes that show up together
- A heater code with P0420: fix the heater fault first; the catalyst test relies on the downstream sensor working properly.
- P0137 with P0171: a genuinely lean exhaust can pull the downstream reading low, so the lean condition may be the cause rather than the sensor.
Oxygen sensors codes
P0141
The heater in the downstream oxygen sensor on bank 1 isn't working as the computer expects
Severity: MonitorP0138
The downstream oxygen sensor on bank 1 is reporting a voltage that stays too high
Severity: MonitorP0137
The downstream oxygen sensor on bank 1 is reporting a voltage that stays too low
Severity: MonitorP0031
The heater control circuit for the upstream oxygen sensor on bank 1 is reading too low
Severity: MonitorP0037
The heater control circuit for the downstream oxygen sensor on bank 1 is reading too low
Severity: MonitorP0131
The engine computer sees a voltage that is too low on the upstream oxygen sensor circuit for bank 1
Severity: MonitorP2196
The upstream oxygen or air-fuel sensor on bank 1 has been reporting a rich mixture for too long, beyond what the engine computer expects
Severity: Inspect soonP0030
Oxygen sensor heater circuit fault on bank 1 sensor 1
Severity: MonitorP0133
Upstream oxygen sensor on bank 1 reacts too slowly
Severity: Severity not verifiedP0140
The oxygen sensor behind the catalytic converter on bank 1 is not sending a signal the computer can use
Severity: MonitorP2195
The upstream oxygen or air-fuel sensor on bank 1 reports a mixture that looks stuck lean or not believable
Severity: Inspect soonP0161
Oxygen sensor heater circuit fault, bank 2 sensor 2
Severity: MonitorP0036
A fault in the heater control circuit of the downstream oxygen sensor on bank 1
Severity: MonitorP0132
Front oxygen sensor signal too high (bank 1, sensor 1)
Severity: MonitorP0136
Rear oxygen sensor circuit fault (bank 1, sensor 2)
Severity: MonitorP015B
Front oxygen sensor slow to respond, lean to rich (bank 1, sensor 1)
Severity: MonitorP2A00
Front air-fuel sensor signal out of range (bank 1, sensor 1)
Severity: Severity not verifiedP0130
The upstream oxygen sensor on bank 1 is sending a signal the computer judges to be wrong
Severity: Severity not verifiedP0134
The upstream oxygen sensor on bank 1 is giving the computer no signal activity
Severity: Severity not verifiedP0139
The rear oxygen sensor on bank 1 reacts too slowly to changes in the exhaust
Severity: MonitorP0142
The bank 1 sensor 3 oxygen sensor circuit is giving the computer a signal outside what it expects
Severity: Severity not verifiedP0143
The bank 1 sensor 3 oxygen sensor is reporting a voltage that is too low
Severity: Severity not verifiedP0144
The bank 1 sensor 3 oxygen sensor is reporting a voltage that is too high
Severity: Severity not verifiedP0145
The oxygen sensor farthest downstream on bank 1 (sensor 3) is responding too slowly
Severity: MonitorP0146
The computer sees no signal from the oxygen sensor farthest downstream on bank 1 (sensor 3)
Severity: MonitorP0147
The heater in the oxygen sensor farthest downstream on bank 1 (sensor 3) is not working as the computer expects
Severity: MonitorP0150
Oxygen sensor circuit fault on the bank 2 upstream sensor
Severity: Severity not verifiedP0151
Bank 2 sensor 1 oxygen sensor signal is lower than the sensor can normally produce
Severity: MonitorP0152
The upstream oxygen sensor on bank 2 is sending a voltage higher than the computer thinks is possible
Severity: Severity not verifiedP0153
The upstream oxygen sensor on bank 2 is slow to react to changes in the exhaust
Severity: MonitorP0154
Bank 2 upstream oxygen sensor not responding
Severity: Severity not verifiedP0155
Heater circuit fault on the upstream oxygen sensor on the second bank of cylinders (bank 2, sensor 1)
Severity: MonitorP0156
The oxygen sensor after the catalytic converter on bank 2 (sensor 2) has a circuit fault
Severity: MonitorP0157
The oxygen sensor after the catalytic converter on bank 2 (sensor 2) is sending a signal voltage that is too low
Severity: MonitorP0158
Oxygen sensor signal voltage reads too high, bank 2 sensor 2
Severity: MonitorP0159
Oxygen sensor responding too slowly, bank 2 sensor 2
Severity: MonitorP0160
Oxygen sensor shows no activity, bank 2 sensor 2
Severity: MonitorP0163
Oxygen sensor signal voltage reads too low, bank 2 sensor 3
Severity: MonitorP0164
Bank 2 sensor 3 oxygen sensor signal is higher than the computer expects
Severity: MonitorP2197
The upstream oxygen or air-fuel sensor on bank 2 is stuck reading lean, or its signal does not make sense
Severity: Inspect soonP0166
Downstream oxygen sensor on bank 2 (sensor 3) is sending no signal activity to the engine computer
Severity: Inspect soon
Sources and review
- Final Regulation Order: 13 CCR §1968.2, Malfunction and Diagnostic System Requirements (OBD II), 2004 and subsequent model-year passenger cars, light-duty trucks and medium-duty vehicles (2015 amendments)
- 40 CFR §86.1806-04 On-board diagnostics (2011 edition page, includes the end of §86.1806-01(k) malfunction criteria)
- OBD: Frequently Asked Questions (EPA420-F-02-014, rev. September 2012)
- Oxygen Sensors (technical PDF)
- Diagnosing Catalytic Converter Problems
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error