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1998 Dodge Dakota P0138 O2 Sensor Error: Shift Issues and Electrical Troubleshooting Guide

Model: 98 Dakota Fault Code: P0138 Posted: 2012-11-18 22:45

I own a 1998 Dodge Dakota with a 5.2L V8 and automatic transmission. The vehicle exhibits erratic shifting behavior—sometimes failing to shift up, causing the engine to run in free-wheel mode, and other times refusing to shift when it should. After taking it to a shop that previously rebuilt my 1996 Dodge CTD’s transmission, they suggested the oxygen (O₂) sensor as the likely cause. They identified a P0138 diagnostic trouble code (DTC): 'O₂ Circuit High Voltage (Bank 1 Sensor 2).' I’ve since confirmed this same error with a new code reader. Bank 1 refers to the driver’s side exhaust catalytic converter, and Sensor 2 is the downstream O₂ sensor—indicating there are actually two catalytic converters and four O₂ sensors in total (not just two as I initially assumed). I’ve purchased a pair of replacement O₂ sensors, but research shows that simply swapping them often doesn’t resolve the issue. The Malfunction Indicator Lamp (MIL) has been on steadily for two weeks, though it briefly turned off yesterday after being cleared with a scanner—only to return shortly afterward. This intermittent MIL behavior, combined with the 'high voltage' P0138 code, leads me to suspect an electrical short in the O₂ sensor circuit. I’m now preparing to use an automotive multimeter to test for voltage and continuity. I’d like input on how to properly troubleshoot the wiring harness and circuits related to the O₂ sensors. Specifically: - Is a short in the heater circuit (which provides 12V) likely? - Are there known issues with pinched, corroded, or damaged wiring behind the catalytic converters? - How can I verify if the sensor is receiving proper power and ground? I’ve also received the vehicle’s factory service manual (FSM), which should help me interpret schematics. I’m now ready to begin hands-on testing with the multimeter and live data monitoring. Additionally, I’ve been advised that the transmission fluid condition may influence shifting—so I plan to perform a full transmission flush as a next step, though I’d like confirmation on proper procedures for this process.

Related fault codes

P0138

Comments (6)

Anonymous 2012-11-19 08:07

The P0138 code could be caused by a short in the heater circuit (which typically provides 12V) migrating into the sensor portion. Check freeze-frame data from your scanner—having 12V on this circuit would confirm it. The O₂ sensor connector has four wires: pin 1 is 12V, pin 2 is ground, pin 3 is 5V, and pin 4 carries a variable signal (usually below 5V). Inspect the wiring harness for damage, pinching, or corrosion—especially behind the catalytic converters. This code is not likely related to transmission shifting.

Anonymous 2012-11-20 07:02

For optimal performance and reliability, purchase O₂ sensors from reputable brands like NTK or the dealership. Avoid generic or aftermarket sensors that may not meet OEM specifications.

Anonymous 2012-11-20 23:02

The FSM arrived last Thursday—just in time! I was concerned it might be delayed due to the holiday, but it shipped promptly. I also ordered a multimeter and received it this week; shipping costs were surprisingly high, so I’ll keep that in mind for future purchases. I initially doubted whether an O₂ sensor could affect transmission shifting—especially since my truck has been a diesel for over 12 years. But after reviewing the forum, I now understand that OBD-I systems like this one can have such connections. With the FSM, I’m starting to go through the electrical schematics to better understand the Dakota’s wiring. I’ve confirmed that the MIL turned off again this evening while driving home—this is unexpected and may indicate a temporary resolution or an underlying issue cycling in and out. @jeff compton: Yes! During my research, I found several references suggesting NGK (or NTK) sensors and plugs are preferred for reliability. The ones I’ve purchased so far are from the NTK brand. I plan to collect freeze-frame data this Friday—thanks for the input! It seems like I asked too soon, but you've already provided valuable insights.

Anonymous 2012-11-21 10:16

The intermittent MIL behavior strongly suggests a wiring issue in the O₂ sensor harness—especially since these sensors are located behind the catalytic converters and are exposed to harsh conditions. Use a digital multimeter (DVOM) to test for voltage while gently shaking the harness. This can help detect loose or corroded connections. Before investing in expensive repairs, compare diagnostic time versus part cost—this 1998 model may have accumulated wear that warrants maintenance over replacement. Quick checks: ensure transmission fluid is at proper level and check for leaks, smell, and color. Also verify the TV (throttle valve) cable—often incorrectly called a 'kick-down' cable—is properly connected. Many owners have found that simply replacing the transmission filter resolves shifting issues. Always use the correct transmission fluid type—Mopars are sensitive to fluid specifications; never use universal fluids.

Anonymous 2012-11-26 20:37

I’ve been monitoring live data with a scan tool for the past four days, especially as temperatures have dropped below freezing (hovering just above 0°F). No moisture has entered the wire bundles—so environmental exposure isn’t likely. The FSM arrived last Thursday. The multimeter is now in my possession and should arrive soon. I’ve also requested a 'build sheet' from Dodge, which was delivered on Saturday—much faster than expected. Based on this, I’m planning to perform a full transmission fluid change with filter replacement using the correct Mopar-specific fluid (not universal). If I feel confident, I’ll add one can of B&G transmission conditioner. I’ve also seen references to 'power flushing' transmissions—however, this is not recommended and should be avoided. It’s often a misleading sales pitch from third-party vendors. PS: Did you check the TV cable? It's critical for proper shifting behavior.

Anonymous 2012-11-27 09:38

Avoid power flushing—it's not an accepted or reliable practice and can cause more harm than good. For your 1998 Dakota, first remove the transmission dipstick to check the recommended fluid type (often labeled on the stick). If it’s missing, consult your build sheet to confirm whether you have a 42RFE or another transmission model. I recommend removing the transmission pan, replacing the filter, and refilling with the correct Mopar-specific transmission fluid. Never use universal fluids—Mopar transmissions are highly sensitive. For added protection, feel free to add one can of appropriate B&G transmission conditioner. PS: Did you check the TV cable? It plays a key role in shifting behavior.