P0138: O2 Sensor Circuit High Voltage Bank 1 Sensor 2
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Yes - same low urgency as P0137.
Symptoms
- Check engine light only in most cases
Likely causes, most common first
- Rear O2 sensor shorted internally
- Wiring chafe to a voltage source
- Genuinely rich exhaust reaching the rear sensor
Read P0138 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0138 is high voltage from the same rear sensor - either an electrical fault or truly rich exhaust making it past the converter. If rich-running codes accompany it, chase those first; the rear sensor may be the only honest witness.
Alone, it is routinely just the sensor. They live in a brutal environment and a decade of service is a full career.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P0138
“Multiple reports of; Codes P0171 System too lean bank 1 P0138 O2 sensor circuit high (b1s2) P0087 Fuel pressure too low P0036 B1S2 *** frequent fuel pump and fuel injector replacements/ services due to defects in the system. Causing major damage in other systems including engine.***”2014 Kia Sorento · Mar 2024
“The contact owns a 2017 Chevrolet Malibu. The contact stated that while driving at an undisclosed speed, the check engine warning light illuminated. The vehicle was taken to an independent mechanic to be diagnosed. The mechanic retrieved fault code: P0138 (engine control module (ECM). The vehicle had unknown repairs completed; however, the failure recurred. The contact made the independent mechanic aware of the failure; however, the vehicle was not taken back to be diagnosed or repaired. The manufacturer was not made aware of the failure. The failure mileage was unknown.”2017 Chevrolet Malibu · Oct 2022
“OBD2 codes ran on vehicle show: P0138 ("O2 sensor circuit High voltage bank 1 sensor 2") P013E (unknown) P2138 ("Throttle/Pedal Position Sensor Switch D/E Voltage Correlation") Vehicle is getting poor fuel mileage and has a drastic delay in acceleration after pressing the gas pedal, putting driver in immediate danger in traffic.”2017 Chevrolet Malibu · May 2021
Show 2 more owner reports
“Ze2 warranty explains as a leaking engine oil cooler pipe A Brief knocking a really niceAt startup in th 1ar2.7l 4-0041-13 Cylinder engine could be caused by probable with the camshaft timing VVT gear assembly My invoice states Knocking rattling noise at start off causes problems with the camshaft time in a gear assembly was repaired February 15 2021 B system warning light is on. Test for stored codes. Misc p0138: tech found internal electrical failures in rear O2 sensor and AF sensor also found internal failures in cam gears replaced all parts .$2168.77 (miles122919)Then it was also done on Oct 30 2018 $1337.73(miles 104725)”2010 Toyota Venza · Feb 2021
“Just had the eniter exaust system replaced due to the cats were plugged . Replaced cats and all o2 sensors with factory oem's and now the car give 3 different codes , p0141, p0138, p1499 . After the codes showed up took back to shop and had to replace all the o2 senors again to the tune of $500.00 plus labor. And went to drive and get tested only to fail again, for bank 1 sensor 2 high voltage detected. Now shop is telling me there was a problem with the pmc and it needs to be replaced to the tune of another $450.00 plus labor.”2002 Jeep Grand Cherokee · Jul 2017 · 126,820 mi
Cars that report P0138 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0138?
Yes - same low urgency as P0137.
How much does it cost to fix P0138?
Typical US repair costs range from $80 for the simplest fix (downstream o2 sensor) to $400 in the worst case. The right number depends on which cause your car has - see the causes list.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.