Q: check engine light on with code P0139 and P0841. Added Techron last fill up and now light went off, on and off again. What is go

asked by on May 08, 2017

check engine light on with code P0139 and P0841. Added Techron during last fill up about 5 days ago and now light went off after driven 30 miles, but it came back on again with another 20 miles. The light went off again this morning after another 40 miles driven. What is going on?

My car has 50000 miles.
My car has an automatic transmission.

The trouble codes that you have downloaded have not arisen due to the use, or non-use, of the fuel additive. Code P0841 simply refers to an abnormality in the transmission fluid pressure sensor circuit. Possible causes of that code include a faulty electronic pressure control solenoid, a defective transmission fluid pressure sensor, blockages inside the internal transmission fluid passages, low transmission fluid or dirty and contaminated transmission fluid and, finally, internal mechanical transmission failure.


The other code, namely P0139 will set if the O2 sensor for bank 1 (sensor 2 on bank 1) fails to report a voltage below .2 volts for 7 seconds during a deceleration fuel cut off. The oxygen sensor itself could be faulty and/or there could be excessive fuel still in the exhaust stream from possible leaking in the fuel injection system.


Both of these codes would have occurred whether you used the fuel system cleaner or not. The reason the codes are appearing intermittently is simply because the failure itself is "intermittent". If you were to wait long enough, whatever component is causing the failure will completely fail and then the engine light will stay on constantly. If you desire a diagnostic covering both codes, performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a check engine light diagnostic and the responding certified mechanic will diagnose the issue(s) and let you know of the required repairs and the cost. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Engine light is on+ VSC Trac lights

The "VSC Trac light on" problem is related to a software problem with the yaw rate sensors calibration. This is documented in Toyota Technical Service Bulletin TSB #BR005-03, which your Toyota service center can apply to re-calibrate this sensor. [Note:...

When turned to the "On" position, there is a clicking noise as if there's a dead battery.

Hello and thank you for contacting YourMechanic. Check the connections from the ignition switch to the starter. It seems to me like there is a short within the ignition switch making the starter engage when the ignition switch is selected...

Engine lost power and now won't start.

Hi there. This can be caused by any number of different problems. Most of the time if the vehicle starts to gradually lose power and then it turns off it is caused by a failing fuel pump. It can be...

Related articles

P3449 OBD-II Trouble Code: Cylinder l7 Deactivation/Intake Valve Control Circuit/Open
P3449 means there is an issue with the Engine Control Module via the intake valve due to low oil pressure, or faulty solenoid.
P0446 OBD-II Trouble Code: Evaporative Emission Control System Vent Control Circuit Malfunction
P0446 code definition P0446 is an OBD2 diagnostic trouble code that indicates a fault within the evaporative emission control system. Other EVAP...
P2125 OBD-II Trouble Code: Throttle/Pedal Position Sensor/Switch "E" Circuit
P2125 P2125 code definition P2125 is a general OBD-II trouble code indicating a fault with the throttle/pedal position sensor/switch “E” circuit. This code is similar to many other throttle body and pedal position codes. What the P2125 code means The...