|Trouble Code||Fault Location||Probable Cause|
|P2626||Heated oxygen sensor (H02S) 1, bank 1, pumping current trim - open circuit / - no signal||Wiring, H025, ECM|
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What Does Code P2626 Mean?
OBD II fault code P2626 is defined as “Oxygen Sensor Pumping Current Trim Circuit Open- Bank1 Sensor 1”, and is set when the PCM Powertrain Control Module) detects a signal voltage from the sensor that falls outside of the accepted, or expected range during deceleration. “Bank 1” refers to the bank of cylinders that contains cylinder #1, and “Sensor 1” refers to the oxygen sensor located before, or upstream of the catalytic converter.
Older, narrow band oxygen sensors and air/fuel ratio sensors react to changing oxygen levels in the exhaust stream by generating signal voltages based on the actual oxygen content of the exhaust stream, but the changes in the signal voltage(s) generated are abrupt when the engine changes from a rich-running, to a lean-running condition, such as during deceleration.
New generation wide-band oxygen sensors and air/fuel ratio sensors do much the same thing, but much more efficiently by virtue of the complex relationships between a wide band oxygen sensors’ actual monitoring cell, the material(s) it’s made from, and some additional electronics in both the sensor and its control circuit.
Taken as a whole, these relationships and interactions work together to compare the actual oxygen content of the exhaust stream to the expected signal voltage (based on the oxygen content) much more accurately, and over a far wider range of signal voltages than was possible before.
Moreover, the resulting signal voltages do not change as abruptly as on narrow band oxygen sensors. Since the pumping circuit is actively moving oxygen into the monitoring cell, the decrease in the oxygen content of the exhaust stream is continuously communicated to the PCM almost in real time.
This has the advantage that the PCM is better able to maintain the air/fuel ratio at the optimum 14.7: 1 level, which improves performance while reducing emissions at the same time. This feature not only makes this type of oxygen sensor more suitable for use on modern, low-emission engines, but also makes tuning adjustments to high-performance engines more predictable.
Typically, code P2626 will be set when the signal voltage from a sensor exceeds the value the PCM expects to receive for a specified period of time, given the current operating conditions and engine load/speed. On most applications, a deviation in both directions of more than 10% from the expected value will set code and illuminate the CHECK ENGINE light, as will a deviation that exceeds a continuous period of about 8 seconds.
NOTE: The actual time it will take before the code sets varies between applications, so be sure to consult the manual for the value specified for the application being worked on.
The image below shows a simplified cutaway of a typical broadband oxygen sensor. Note the location of the pumping cell that “pumps” oxygen ions towards the measurement chamber. The pumping action of the pump cell is wholly dependent on the heater element heating, and maintaining, the sensor at a specific temperature.
What are the common causes of code P2626?
Some common causes of code P2626 could include the following-
Defective oxygen or air/fuel ratio sensor.
Damaged, burnt, shorted, or corroded wiring and/or connectors.
Blown “trim” or “calibration” resistors on some applications.
Excessive oil consumption (Note that “excessive” is a relative term in this context; some engines, for instance some BMW engines, can use as much as 1 quart of oil per 1 000 miles or less, which is considered to be within normal limits for these engines. Expect a higher-than-average incidence of code P2626 on these engines.
Some aftermarket oil and fuel additives can form harmful deposits on sensors.
Failed, or failing PCM. This is a rare event, and the fault must be sought elsewhere before any controller is replaced.
What are the symptoms of code P2626?
Although the symptoms of code P2626 are much the same on all applications, the severity of one or more symptoms may vary between applications. Typical symptoms of code P2626 could include the following-
- Stored trouble code and illuminated CHECK ENGINE warning light
- Increased fuel consumption
- Rich, or lean running condition may be present
- Visible black smoke from the tail pipe
- Loss of engine power
- Hesitation upon acceleration
How do you troubleshoot code P2626?
NOTE: While the inner working of oxygen sensors is a highly technical subject, the “Pumping Circuit” in this code refers to the sensors’ ability to move, or “pump” oxygen towards the actual monitoring unit, which makes it possible to monitor the oxygen content of the exhaust stream more accurately when sudden changes in the air/fuel ratio occur. In the majority of cases, replacement of the affected sensor will cure the problem.
SPECIAL NOTES: Diagnosing code P2626 can be particularly challenging in some cases, hence the additional information supplied here. Note that despite this information, the manual for the application being worked on should always be consulted for the exact electrical values for that particular application.
The LAF (Lean Air/Fuel) sensors on many Honda models use a special calibration resistor that is located in the 8-pin connector, between pins 3 and 4. Depending on the application, the resistance across this resistor can have one of three values; 2.4K ohm, 10K ohm, or 15K ohm. If the connector has to be replaced for any reason, make sure that the resistor in the replacement connector has exactly the same resistance. Note that the reference voltage on these engines is supplied by the PCM, and should be 2.7 Volts.
Some Saturn (GM) models also incorporate a “trim” resistor in the wide band oxygen sensor connector, between pins 1 and 6. The accepted resistance range for this resistor should be above 30 ohm, but below 300 ohm. The reference voltage is also supplied by the PCM, and should be between 2.4-, and 2.6 Volts.
On some early Toyota applications, the Air/Fuel sensor will supply a “simulated” oxygen sensor signal voltage that can appear to be wildly inaccurate. However, to comply with early OBD II regulations, the actual signal voltage generated by the A/F sensor on these applications is divided by 5 to make it readable on early scanners, so keep this fact in mind when a scanner displays a seemingly impossible reading.
Code P2626 has a relatively high incidence on vehicles that use more oil than normal, among which vehicles BMW tops the list. However, the incidence of this code on oil-guzzling vehicles can be reduced somewhat by only using the best quality engine oil and fuel.
Record all fault codes and available freeze frame data. This information can be helpful should an intermittent fault be diagnosed later on.
NOTE: As with all other oxygen sensor related codes, diagnosing code P2626 requires that the engine be in perfect running condition. There should be no misfiring, lean-, or rich running conditions present, nor should there be vacuum system issues, or exhaust leaks present that could interfere with the proper operation of oxygen or air/fuel ratio sensors. If any codes other than P2626 are present, these codes should be resolved before starting a diagnostic procedure for code P2626.
Perform a thorough visual inspection of all wiring associated with the affected sensor. Consult the manual to determine the color-coding, location, routing, and function of each wire and look for damaged, burnt, shorted, or corroded wiring and connectors. Resist the temptation to repair wiring; the better option is always to replace wiring to prevent potential problems with resistance and continuity on poorly executed repairs.
NOTE: Refer to the additional notes at the top of this section if the application being worked on has “trim”, or “calibration” resistors.
If there is no visible damage to wiring and connectors perform resistance, continuity, ground, and reference voltage checks on all associated wiring. Take note that since the heater element in a sensor largely determines how well the sensor works, pay particular attention to the heater circuit.
Regardless of whether the heater input voltage is supplied through a fused circuit or by the PCM, the obtained reading should match the value stated in the manual exactly. Small variations in the heater circuit input voltage can affect the overall functioning of the pumping circuit in the sensor, so make sure there are no issues with the heater circuit.
NOTE: Be sure to disconnect the sensor from the PCM before starting resistance and continuity checks on the wiring to prevent damage to the controller.
Once repairs to wiring had been made, clear the code and test drive the vehicle with a scanner connected to monitor the working of the sensor in real time. The signal voltage from the sensor should change constantly, from around 100 millivolts, to around 900 millivolts. However, to get the most accurate results, set the scanner to only monitor the affected sensor.
If the code returns, or the sensor returns invalid data, or if there are significant time lags between changes in the signal voltage, remove the sensor and test its internal resistance. Consult the manual for the exact resistance value, and replace the sensor if the resistance does not fall within the manufacturer’s specifications.
In most cases, replacing the sensor if the wiring checks out OK will cure the problem, but operate the vehicle again after the sensor replacement to verify that the repair had been successful.
NOTE: To avoid a speedy recurrence of code P2626, inspect the old sensor for signs of discoloration or the presence of any type of deposit on any part of the sensor. As stated before, excessive oil consumption can foul the sensing elements of the sensor, but so can some aftermarket oil and fuel additives that contain silicone-based compounds.
The image below shows the typical appearance of sensors that are fouled with oil or other compounds. If any evidence of this is found, discontinue the use of all additives, and investigate the cause of excessive oil burning. An oil-fouled sensor (not shown here) will typically be covered with a black, tarry substance.
Codes Related to P2626
Note that code P2626 does not mean the same thing to all manufacturers. Moreover, this code does not appear on all lists of generic codes; therefore, it is recommended that an online search be performed for the exact definition of a code (relating to the application being worked on) whenever the words “Oxygen Sensor Pumping Circuit” appear in the code definition on a scanner.