3 steps to diagnose easily Oxygen sensor troubles - Troubleshooting Diesel engine problems

You are suspecting the oxygen sensor to be faulty but you are still not sure? Following these three simples steps will help you to get a clear statement.

Warning!

Disclaimer: This site and the author are not responsible of any misuse of the provided information. The information is only given to help for fault diagnosis. Injuries, electric shocks, burns and other life threatening hazards can be a result of an inappropriate action on the engine. If you are not familiar with engines and not sensitized to the safety procedures, please contact a professional. Any action on the car and its consequences are under your sole responsability.

Contents

Use of a diagnosis tool to troubleshoot oxygen sensor problems

The following P-codes (DTCs) are OBD II failure codes and generic to all OBD II compatible cars and could appear, if your oxygen sensor is faulty. Please note that the contrary is not true. The appearance of these faults does not mean that the sensor is faulty and could be a result of a failure in the other elements of the sensor circuit (cables, ECU, …) or in the mechanical part of the combustion system.

System	DTC	Description
Powertrain	P0030	HO2S Heater Control Circuit Bank 1 Sensor 1
Powertrain	P0031	HO2S Heater Control Circuit Low Bank 1 Sensor 1
Powertrain	P0032	HO2S Heater Control Circuit High Bank 1 Sensor 1
Powertrain	P0036	HO2S Heater Control Circuit Bank 1 Sensor 2
Powertrain	P0037	HO2S Heater Control Circuit Low Bank 1 Sensor 2
Powertrain	P0038	HO2S Heater Control Circuit High Bank 1 Sensor 2
Powertrain	P0040	O2 Sensor Signals Swapped Bank 1 Sensor 1/Bank 2 Sensor 1
Powertrain	P0041	O2 Sensor Signals Swapped Bank 1 Sensor 2/Bank 2 Sensor 2
Powertrain	P0042	HO2S Heater Control Circuit Bank 1 Sensor 3
Powertrain	P0043	HO2S Heater Control Circuit Low Bank 1 Sensor 3
Powertrain	P0044	HO2S Heater Control Circuit High Bank 1 Sensor 3
Powertrain	P0050	HO2S Heater Control Circuit Bank 2 Sensor 1
Powertrain	P0051	HO2S Heater Control Circuit Low Bank 2 Sensor 1
Powertrain	P0052	HO2S Heater Control Circuit High Bank 2 Sensor 1
Powertrain	P0053	HO2S Heater Resistance Bank 1 Sensor 1
Powertrain	P0054	HO2S Heater Resistance Bank 1 Sensor 2
Powertrain	P0055	HO2S Heater Resistance Bank 1 Sensor 3
Powertrain	P0056	HO2S Heater Control Circuit Bank 2 Sensor 2
Powertrain	P0057	HO2S Heater Control Circuit Low Bank 2 Sensor 2
Powertrain	P0058	HO2S Heater Control Circuit High Bank 2 Sensor 2
Powertrain	P0059	HO2S Heater Resistance Bank 2 Sensor 1
Powertrain	P0060	HO2S Heater Resistance Bank 2 Sensor 2
Powertrain	P0061	HO2S Heater Resistance Bank 2 Sensor 3
Powertrain	P0062	HO2S Heater Control Circuit Bank 2 Sensor 3
Powertrain	P0063	HO2S Heater Control Circuit Low Bank 2 Sensor 3
Powertrain	P0064	HO2S Heater Control Circuit High Bank 2 Sensor 3
Powertrain	P00D1	HO2S Heater Control Circuit Range/Performance Bank 1 Sensor 1
Powertrain	P00D2	HO2S Heater Control Circuit Range/Performance Bank 1 Sensor 2
Powertrain	P00D3	HO2S Heater Control Circuit Range/Performance Bank 2 Sensor 1
Powertrain	P00D4	HO2S Heater Control Circuit Range/Performance Bank 2 Sensor 2
Powertrain	P00D5	HO2S Sensor Correlation Bank 1 Sensor 1/Bank 1 Sensor 2
Powertrain	P00D6	HO2S Sensor Correlation Bank 2 Sensor 1/Bank 2 Sensor 2
Powertrain	P0130	O2 Sensor Circuit Bank 1 Sensor 1
Powertrain	P0131	O2 Sensor Circuit Low Voltage Bank 1 Sensor 1
Powertrain	P0132	O2 Sensor Circuit High Voltage Bank 1 Sensor 1
Powertrain	P0133	O2 Sensor Circuit Slow Response Bank 1 Sensor 1
Powertrain	P0134	O2 Sensor Circuit No Activity Detected Bank 1 Sensor 1
Powertrain	P0135	O2 Sensor Heater Circuit Bank 1 Sensor 1
Powertrain	P0136	O2 Sensor Circuit Bank 1 Sensor 2
Powertrain	P0137	O2 Sensor Circuit Low Voltage Bank 1 Sensor 2
Powertrain	P0138	O2 Sensor Circuit High Voltage Bank 1 Sensor 2
Powertrain	P0139	O2 Sensor Circuit Slow Response Bank 1 Sensor 2
Powertrain	P013A	O2 Sensor Slow Response - Rich to Lean Bank 1 Sensor 2
Powertrain	P013B	O2 Sensor Slow Response - Lean to Rich Bank 1 Sensor 2
Powertrain	P013C	O2 Sensor Slow Response - Rich to Lean Bank 2 Sensor 2
Powertrain	P013D	O2 Sensor Slow Response - Lean to Rich Bank 2 Sensor 2
Powertrain	P013E	O2 Sensor Delayed Response - Rich to Lean Bank 1 Sensor 2
Powertrain	P013F	O2 Sensor Delayed Response - Lean to Rich Bank 1 Sensor 2
Powertrain	P0140	O2 Sensor Circuit No Activity Detected Bank 1 Sensor 2
Powertrain	P0141	O2 Sensor Heater Circuit Bank 1 Sensor 2
Powertrain	P0142	O2 Sensor Circuit Bank 1 Sensor 3
Powertrain	P0143	O2 Sensor Circuit Low Voltage Bank 1 Sensor 3
Powertrain	P0144	O2 Sensor Circuit High Voltage Bank 1 Sensor 3
Powertrain	P0145	O2 Sensor Circuit Slow Response Bank 1 Sensor 3
Powertrain	P0146	O2 Sensor Circuit No Activity Detected Bank 1 Sensor 3
Powertrain	P0147	O2 Sensor Heater Circuit Bank 1 Sensor 3
Powertrain	P014A	O2 Sensor Delayed Response - Rich to Lean Bank 2 Sensor 2
Powertrain	P014B	O2 Sensor Delayed Response - Lean to Rich Bank 2 Sensor 2
Powertrain	P014C	O2 Sensor Slow Response - Rich to Lean Bank 1 Sensor 1
Powertrain	P014D	O2 Sensor Slow Response - Lean to Rich Bank 1 Sensor 1
Powertrain	P014E	O2 Sensor Slow Response - Rich to Lean Bank 2 Sensor 1
Powertrain	P014F	O2 Sensor Slow Response - Lean to Rich Bank 2 Sensor 1
Powertrain	P0150	O2 Sensor Circuit Bank 2 Sensor 1
Powertrain	P0151	O2 Sensor Circuit Low Voltage Bank 2 Sensor 1
Powertrain	P0152	O2 Sensor Circuit High Voltage Bank 2 Sensor 1
Powertrain	P0153	O2 Sensor Circuit Slow Response Bank 2 Sensor 1
Powertrain	P0154	O2 Sensor Circuit No Activity Detected Bank 2 Sensor 1
Powertrain	P0155	O2 Sensor Heater Circuit Bank 2 Sensor 1
Powertrain	P0156	O2 Sensor Circuit Bank 2 Sensor 2
Powertrain	P0157	O2 Sensor Circuit Low Voltage Bank 2 Sensor 2
Powertrain	P0158	O2 Sensor Circuit High Voltage Bank 2 Sensor 2
Powertrain	P0159	O2 Sensor Circuit Slow Response Bank 2 Sensor 2
Powertrain	P015A	O2 Sensor Delayed Response - Rich to Lean Bank 1 Sensor 1
Powertrain	P015B	O2 Sensor Delayed Response - Lean to Rich Bank 1 Sensor 1
Powertrain	P015C	O2 Sensor Delayed Response - Rich to Lean Bank 2 Sensor 1
Powertrain	P015D	O2 Sensor Delayed Response - Lean to Rich Bank 2 Sensor 1
Powertrain	P0160	O2 Sensor Circuit No Activity Detected Bank 2 Sensor 2
Powertrain	P0161	O2 Sensor Heater Circuit Bank 2 Sensor 2
Powertrain	P0162	O2 Sensor Circuit Bank 2 Sensor 3
Powertrain	P0163	O2 Sensor Circuit Low Voltage Bank 2 Sensor 3
Powertrain	P0164	O2 Sensor Circuit High Voltage Bank 2 Sensor 3
Powertrain	P0165	O2 Sensor Circuit Slow Response Bank 2 Sensor 3
Powertrain	P0166	O2 Sensor Circuit No Activity Detected Bank 2 Sensor 3
Powertrain	P0167	O2 Sensor Heater Circuit Bank 2 Sensor 3
Powertrain	P019A	O2 Sensor Delayed Response - Rich to Lean Bank 1 Sensor 3
Powertrain	P019B	O2 Sensor Delayed Response - Lean to Rich Bank 1 Sensor 3
Powertrain	P019C	O2 Sensor Delayed Response - Rich to Lean Bank 2 Sensor 3
Powertrain	P019D	O2 Sensor Delayed Response - Lean to Rich Bank 2 Sensor 3
Powertrain	P01F1	O2 Sensor Circuit Bank 1 Sensor 4
Powertrain	P01F2	O2 Sensor Circuit Low Voltage Bank 1 Sensor 4
Powertrain	P01F3	O2 Sensor Circuit High Voltage Bank 1 Sensor 4
Powertrain	P01F4	O2 Sensor Circuit Slow Response Bank 1 Sensor 4
Powertrain	P01F5	O2 Sensor Circuit No Activity Detected Bank 1 Sensor 4
Powertrain	P01F6	O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 4
Powertrain	P01F7	O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 4
Powertrain	P055E	Oxygen Sensor Control Module System Voltage
Powertrain	P064D	Internal Control Module O2 Sensor Processor Performance Bank 1
Powertrain	P064E	Internal Control Module O2 Sensor Processor Performance Bank 2
Powertrain	P2195	O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 1
Powertrain	P2196	O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 1
Powertrain	P2197	O2 Sensor Signal Biased/Stuck Lean Bank 2 Sensor 1
Powertrain	P2198	O2 Sensor Signal Biased/Stuck Rich Bank 2 Sensor 1
Powertrain	P2231	O2 Sensor Signal Circuit Shorted to Heater Circuit Bank 1 Sensor 1
Powertrain	P2232	O2 Sensor Signal Circuit Shorted to Heater Circuit Bank 1 Sensor 2
Powertrain	P2233	O2 Sensor Signal Circuit Shorted to Heater Circuit Bank 1 Sensor 3
Powertrain	P2234	O2 Sensor Signal Circuit Shorted to Heater Circuit Bank 2 Sensor 1
Powertrain	P2235	O2 Sensor Signal Circuit Shorted to Heater Circuit Bank 2 Sensor 2
Powertrain	P2236	O2 Sensor Signal Circuit Shorted to Heater Circuit Bank 2 Sensor 3
Powertrain	P2237	O2 Sensor Positive Current Control Circuit/Open Bank 1 Sensor 1
Powertrain	P2238	O2 Sensor Positive Current Control Circuit Low Bank 1 Sensor 1
Powertrain	P2239	O2 Sensor Positive Current Control Circuit High Bank 1 Sensor 1
Powertrain	P223C	O2 Sensor Pumping Current Range/Performance Bank 1
Powertrain	P223D	O2 Sensor Pumping Current Range/Performance Bank 2
Powertrain	P223E	O2 Sensor Reference Resistance Out Of Range Bank 1
Powertrain	P223F	O2 Sensor Reference Resistance Out Of Range Bank 2
Powertrain	P2240	O2 Sensor Positive Current Control Circuit/Open Bank 2 Sensor 1
Powertrain	P2241	O2 Sensor Positive Current Control Circuit Low Bank 2 Sensor 1
Powertrain	P2242	O2 Sensor Positive Current Control Circuit High Bank 2 Sensor 1
Powertrain	P2243	O2 Sensor Reference Voltage Circuit/Open Bank 1 Sensor 1
Powertrain	P2244	O2 Sensor Reference Voltage Performance Bank 1 Sensor 1
Powertrain	P2245	O2 Sensor Reference Voltage Circuit Low Bank 1 Sensor 1
Powertrain	P2246	O2 Sensor Reference Voltage Circuit High Bank 1 Sensor 1
Powertrain	P2247	O2 Sensor Reference Voltage Circuit/Open Bank 2 Sensor 1
Powertrain	P2248	O2 Sensor Reference Voltage Performance Bank 2 Sensor 1
Powertrain	P2249	O2 Sensor Reference Voltage Circuit Low Bank 2 Sensor 1
Powertrain	P2250	O2 Sensor Reference Voltage Circuit High Bank 2 Sensor 1
Powertrain	P2251	O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1
Powertrain	P2252	O2 Sensor Negative Current Control Circuit Low Bank 1 Sensor 1
Powertrain	P2253	O2 Sensor Negative Current Control Circuit High Bank 1 Sensor 1
Powertrain	P2254	O2 Sensor Negative Current Control Circuit/Open Bank 2 Sensor 1
Powertrain	P2255	O2 Sensor Negative Current Control Circuit Low Bank 2 Sensor 1
Powertrain	P2256	O2 Sensor Negative Current Control Circuit High Bank 2 Sensor 1
Powertrain	P2270	O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 2
Powertrain	P2271	O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 2
Powertrain	P2272	O2 Sensor Signal Biased/Stuck Lean Bank 2 Sensor 2
Powertrain	P2273	O2 Sensor Signal Biased/Stuck Rich Bank 2 Sensor 2
Powertrain	P2274	O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 3
Powertrain	P2275	O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 3
Powertrain	P2276	O2 Sensor Signal Biased/Stuck Lean Bank 2 Sensor 3
Powertrain	P2277	O2 Sensor Signal Biased/Stuck Rich Bank 2 Sensor 3
Powertrain	P2278	O2 Sensor Signals Swapped Bank 1 Sensor 3/Bank 2 Sensor 3
Powertrain	P2297	O2 Sensor Out of Range During Deceleration Bank 1 Sensor 1
Powertrain	P2298	O2 Sensor Out of Range During Deceleration Bank 2 Sensor 1
Powertrain	P22AB	O2 Sensor Positive Current Control Circuit/Open Bank 1 Sensor 2
Powertrain	P22AC	O2 Sensor Positive Current Control Circuit Low Bank 1 Sensor 2
Powertrain	P22AD	O2 Sensor Positive Current Control Circuit High Bank 1 Sensor 2
Powertrain	P22AE	O2 Sensor Reference Voltage Circuit/Open Bank 1 Sensor 2
Powertrain	P22AF	O2 Sensor Reference Voltage Performance Bank 1 Sensor 2
Powertrain	P22B0	O2 Sensor Reference Voltage Circuit Low Bank 1 Sensor 2
Powertrain	P22B1	O2 Sensor Reference Voltage Circuit High Bank 1 Sensor 2
Powertrain	P22B2	O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 2
Powertrain	P22B3	O2 Sensor Negative Current Control Circuit Low Bank 1 Sensor 2
Powertrain	P22B4	O2 Sensor Negative Current Control Circuit High Bank 1 Sensor 2
Powertrain	P22B5	O2 Sensor Pumping Current Trim Circuit/Open Bank 1 Sensor 2
Powertrain	P22B6	O2 Sensor Pumping Current Trim Circuit Low Bank 1 Sensor 2
Powertrain	P22B7	O2 Sensor Pumping Current Trim Circuit High Bank 1 Sensor 2
Powertrain	P22B8	O2 Sensor Positive Current Control Circuit/Open Bank 2 Sensor 2
Powertrain	P22B9	O2 Sensor Positive Current Control Circuit Low Bank 2 Sensor 2
Powertrain	P22BA	O2 Sensor Positive Current Control Circuit High Bank 2 Sensor 2
Powertrain	P22BB	O2 Sensor Reference Voltage Circuit/Open Bank 2 Sensor 2
Powertrain	P22BC	O2 Sensor Reference Voltage Performance Bank 2 Sensor 2
Powertrain	P22BD	O2 Sensor Reference Voltage Circuit Low Bank 2 Sensor 2
Powertrain	P22BE	O2 Sensor Reference Voltage Circuit High Bank 2 Sensor 2
Powertrain	P22BF	O2 Sensor Negative Current Control Circuit/Open Bank 2 Sensor 2
Powertrain	P22C0	O2 Sensor Negative Current Control Circuit Low Bank 2 Sensor 2
Powertrain	P22C1	O2 Sensor Negative Current Control Circuit High Bank 2 Sensor 2
Powertrain	P22C2	O2 Sensor Pumping Current Trim Circuit/Open Bank 2 Sensor 2
Powertrain	P22C3	O2 Sensor Pumping Current Trim Circuit Low Bank 2 Sensor 2
Powertrain	P22C4	O2 Sensor Pumping Current Trim Circuit High Bank 2 Sensor 2
Powertrain	P2414	O2 Sensor Exhaust Sample Error Bank 1 Sensor 1
Powertrain	P2415	O2 Sensor Exhaust Sample Error Bank 2 Sensor 1
Powertrain	P2416	O2 Sensor Signals Swapped Bank 1 Sensor 2/Bank 1 Sensor 3
Powertrain	P2417	O2 Sensor Signals Swapped Bank 2 Sensor 2/Bank 2 Sensor 3
Powertrain	P241A	O2 Sensor Signals Swapped Bank 1 Sensor 1/Bank 1 Sensor 2
Powertrain	P241B	O2 Sensor Signals Swapped Bank 2 Sensor 1/Bank 2 Sensor 2
Powertrain	P2626	O2 Sensor Pumping Current Trim Circuit/Open Bank 1 Sensor 1
Powertrain	P2627	O2 Sensor Pumping Current Trim Circuit Low Bank 1 Sensor 1
Powertrain	P2628	O2 Sensor Pumping Current Trim Circuit High Bank 1 Sensor 1
Powertrain	P2629	O2 Sensor Pumping Current Trim Circuit/Open Bank 2 Sensor 1
Powertrain	P2630	O2 Sensor Pumping Current Trim Circuit Low Bank 2 Sensor 1
Powertrain	P2631	O2 Sensor Pumping Current Trim Circuit High Bank 2 Sensor 1
Powertrain	P2A00	O2 Sensor Circuit Range/Performance Bank 1 Sensor 1
Powertrain	P2A01	O2 Sensor Circuit Range/Performance Bank 1 Sensor 2
Powertrain	P2A02	O2 Sensor Circuit Range/Performance Bank 1 Sensor 3
Powertrain	P2A03	O2 Sensor Circuit Range/Performance Bank 2 Sensor 1
Powertrain	P2A04	O2 Sensor Circuit Range/Performance Bank 2 Sensor 2
Powertrain	P2A05	O2 Sensor Circuit Range/Performance Bank 2 Sensor 3
Powertrain	P2A06	O2 Sensor Negative Voltage Bank 1 Sensor 1
Powertrain	P2A07	O2 Sensor Negative Voltage Bank 1 Sensor 2
Powertrain	P2A08	O2 Sensor Negative Voltage Bank 1 Sensor 3
Powertrain	P2A09	O2 Sensor Negative Voltage Bank 2 Sensor 1
Powertrain	P2A10	O2 Sensor Negative Voltage Bank 2 Sensor 2
Powertrain	P2A11	O2 Sensor Negative Voltage Bank 2 Sensor 3
Powertrain	P2A38	O2 Sensor Positive Current Control Circuit/Open Bank 1 Sensor 3
Powertrain	P2A39	O2 Sensor Positive Current Control Circuit Low Bank 1 Sensor 3
Powertrain	P2A3A	O2 Sensor Positive Current Control Circuit High Bank 1 Sensor 3
Powertrain	P2A3B	O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 3
Powertrain	P2A3C	O2 Sensor Negative Current Control Circuit Low Bank 1 Sensor 3
Powertrain	P2A3D	O2 Sensor Negative Current Control Circuit High Bank 1 Sensor 3
Powertrain	P2ABF	Intake Air O2 Sensor Reference Voltage Circuit/Open Bank 1
Powertrain	P2AC0	Intake Air O2 Sensor Reference Voltage Circuit Range/Performance Bank 1
Powertrain	P2AC1	Intake Air O2 Sensor Reference Voltage Circuit Low Bank 1
Powertrain	P2AC2	Intake Air O2 Sensor Reference Voltage Circuit High Bank 1
Powertrain	P2AC3	Intake Air O2 Sensor Reference Voltage Circuit/Open Bank 2
Powertrain	P2AC4	Intake Air O2 Sensor Reference Voltage Circuit Range/Performance Bank 2
Powertrain	P2AC5	Intake Air O2 Sensor Reference Voltage Circuit Low Bank 2
Powertrain	P2AC6	Intake Air O2 Sensor Reference Voltage Circuit High Bank 2
Powertrain	P2AE0	Intake Air O2 Sensor Pumping Current Trim Circuit Open Bank 1
Powertrain	P2AE1	Intake Air O2 Sensor Pumping Current Trim Circuit Low Bank 1
Powertrain	P2AE2	Intake Air O2 Sensor Pumping Current Trim Circuit High Bank 1
Powertrain	P2AE3	Intake Air O2 Sensor Pumping Current Circuit Open Bank 1
Powertrain	P2AE4	Intake Air O2 Sensor Pumping Current Circuit Low Bank 1
Powertrain	P2AE5	Intake Air O2 Sensor Pumping Current Circuit High Bank 1
Powertrain	P2AE6	Intake Air O2 Sensor Negative Current Control Circuit Open Bank 1
Powertrain	P2AE7	Intake Air O2 Sensor Negative Current Control Circuit Low Bank 1
Powertrain	P2AE8	Intake Air O2 Sensor Negative Current Control Circuit High Bank 1
Powertrain	P2AE9	Intake Air O2 Sensor Pumping Current Trim Circuit Open Bank 2
Powertrain	P2AEA	Intake Air O2 Sensor Pumping Current Trim Circuit Low Bank 2
Powertrain	P2AEB	Intake Air O2 Sensor Pumping Current Trim Circuit High Bank 2
Powertrain	P2AEC	Intake Air O2 Sensor Pumping Current Circuit Open Bank 2
Powertrain	P2AED	Intake Air O2 Sensor Pumping Current Circuit Low Bank 2
Powertrain	P2AEE	Intake Air O2 Sensor Pumping Current Circuit High Bank 2
Powertrain	P2AEF	Intake Air O2 Sensor Negative Current Control Circuit Open Bank 2
Powertrain	P2AF0	Intake Air O2 Sensor Negative Current Control Circuit Low Bank 2
Powertrain	P2AF1	Intake Air O2 Sensor Negative Current Control Circuit High Bank 2

In addition to these DTCs, other manufacturer specific DTCs (P1XXX) can also pop-up. These codes will be displayed with a description string while using the scan tool.

Last but not least, you can read the sensor values using the scan tool and look for variations. The oxygen value is an image of the air/fuel ratio and it is for this reason that the sensor is referred as a lambda sensor. This value is usually controlled and follows the setpoint required by the ECU.

Electrical tests of the oxygen sensor

The oxygen sensors are usually made upon one of these sensing elements

chemo-voltaic
chemo-resistive

Please note that usually cars are equipped with two oxygen sensors. The first is installed at the engine outlet and the second at the catalyst downstream. The second sensor allow to evaluate the efficiency of the catalyst and should show, in normal operation, smaller voltage values compared to the sensor installed at the engine outlet.

The chemo-voltaic oxygen sensor

The chemo-voltaic variant is usually a four wire sensor and in some cases, can have three wires. Two wires are used to supply the sensor heater and the two others provide the measurements. Some old sensors are not heated and consequently can have only two wires.

The oxygen sensor has zirconia (ZrO2) sensing element, which outputs voltage variations as a result of a change in the relative oxygen pressure in the exhaust pipe (compared to the normal pressure in the atmosphere). The sensor can give correct values, only when the temperature is in a certain range, generally between 300 and 850°C. This condition is actually guaranteed by the heating element. In a normal engine operation, the controller is changing the fuel quantity, aiming to reach the lambda setpoint. This results in a pseudo-sinusoidal voltage form at the sensor output, oscillating between ~0,2 and ~0,8V.

Moreover, there are more accurate sensors, which belong to this category, called wideband O2 sensors. They usually have five or six wires and require a complicated control strategy to allow acquiring the measurement.

The chemo-resistive oxygen sensor

The chemo-resistive variant is usually a four wire sensor. One wire is used to supply the sensor, the second provides the measurements and the third is the ground. The sensor has additionally a fourth wire to supply the sensor heater. Some old models are not heated and therefore have only three wires. The sensor has titania (titanium oxide) sensing element, which seems to have a shorter time response as the chemo-voltaic variant. The operating principle of the sensor is the same. It outputs voltage variations as a result of a change in the oxygen relative pressure at the exhaust pipe (compared to the normal pressure in the atmosphere). This sensor, as the previous one, uses a heating element to keep the temperature in the range needed for normal operation. The signal output form is similar to the output of the previous sensor. However, it is oscillating between approximately 0,5 and 4V.

Precision test

This test is actually very important, because not having a DTC, doesn’t mean that your oxygen sensor is working without trouble. Many contaminated or used oxygen sensors still show values at their output. Their value accuracy and the speed of value change (frequency), however, are degraded. This can be noted by checking the sensor at its limits (lean and rich lambda). The limits of a new sensor are higher, in both directions, compared to an old sensor. This means, for example for a zirconia sensor, that an old sensor cannot go below 0,2V and beyond 0,8V, where a new sensor can show values lower than 0,1V and higher than 0,9V. To do this, you have for example to trick the ECU, by simulating a lean/rich lambda at its input. The ECU will automatically try to correct the issue, by going in the other lambda direction. Then you can see to which extent the reading performed by your sensor can go (by using a digital multimeter/oscilloscope for example). Please refer to the service manual of your car and respect the instructions and the specified voltages to avoid damaging the ECU or other components.

This method needs unfortunately to have a new oxygen sensor to make the comparison with the values read from the old sensor, otherwise you’re only guessing.