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1997 Dodge Dakota Automatic Transmission Shifting Problems with P0138 O2 Sensor Code

Model: 1997 Dodge Dakota Fault Code: P0138 Posted: 2016-04-27 09:37

I own a 1997 Dodge Dakota Sport with a 3.9L engine. I'm experiencing persistent shifting issues and the check engine light is on. After replacing the throttle position sensor (TPS), the light turned off for a few hours before returning. I then replaced the governor sensor and transmission pressure solenoid, which temporarily resolved the issue—shifting improved and the check engine light stayed off for several days. However, after that period, the check engine light came back on. A diagnostic scan revealed code P0138 (Bank 1 Sensor 2 - Oxygen Sensor Heater Circuit Malfunction). I replaced the oxygen sensor, but the issue returned within less than a day. The scanner now shows additional monitor errors: Catalyst Monitor Incorrect, Oxygen Sensor Monitor Incorrect, and Oxygen Sensor Heater Monitor Incorrect. The only components not yet replaced are the transmission speed sensor and the Powertrain Control Module (PCM). My mechanic team is unable to identify the root cause. Is this an electrical issue or a transmission problem? Has anyone else experienced similar issues with their 1997 Dodge Dakota, particularly with the 42RE transmission? The shifting behavior varies: when the engine is warm, shifting feels normal; however, below 32°F (0°C), the truck often fails to downshift properly—sometimes staying in a higher gear or even appearing to kick into neutral. As temperature increases, the shifting improves. I replaced the oxygen sensor based on the scanner indicating high voltage, but I never measured the actual signal voltage from the sensor. Could this be a misdiagnosis? What should I check next? Is it possible that the catalytic converter is contributing to the issue? Additionally, I’ve had this truck since new and stored it during a cold winter season—could temperature exposure or age-related wear have triggered these symptoms?

Related fault codes
P0138
Comments (7)
Anonymous 2016-04-27 10:05

Are you using an OBD2 scanner? Please post all diagnostic codes. Describe the shifting behavior in detail. Why was the B1S2 oxygen sensor replaced? When you tested the sensor signal voltage, what value did you observe? Share all relevant codes so we can analyze them one by one. Note: Monitor errors like 'incorrect' typically indicate incomplete or failed monitors—after clearing codes, they may switch to 'incomplete'.

Anonymous 2016-04-27 11:40

Yes, we used an OBD2 scanner and the only persistent code is P0138. When the engine is warm, shifting works fine. The issues occur primarily when temperatures drop below 32°F (0°C). The truck sometimes stays in a higher gear or appears to shift into neutral unexpectedly. As it warms up, shifting returns to normal. We replaced the B1S2 oxygen sensor because the scanner showed high voltage—however, we never measured the actual signal voltage. We cleared the codes, which may explain why some monitors now show 'incomplete'.

Anonymous 2016-04-27 12:06

Could a failing catalytic converter be contributing to this issue?

Anonymous 2016-04-27 13:38

There's no strong evidence linking the catalytic converter directly to P0138 or shifting issues. Have you confirmed which transmission model you have? I believe it’s a 42RE—this transmission is not electrically shifted except for 4th gear and torque converter clutch (TCC). After replacing the TPS, it's worth adjusting the Throttle Valve Cable (TVC)—often incorrectly referred to as 'kick-down cable'. The 42RE uses only ATF4 fluid; using Dexron or universal fluids can cause performance issues. A clean transmission filter and fresh ATF4 fluid are recommended. If these steps don’t resolve the issue, transmission pressure testing may be necessary. Tip: Search for 'Dodge 42RE TV cable adjustment' to find tutorials—many Jeep-related videos might also help, as this is a common transmission design. Confirm whether you have a 42RE or another variant.

Anonymous 2016-04-27 15:25

The catalytic converter was part of the original setup and has been in place since new—there’s no clear reason to suspect it as the cause. I do have a 42RE transmission, and both the filter and fluid are clean and up to date. Could the MAP sensor be involved? The issue started after winter storage, so temperature exposure may have contributed to wear or sensor drift. I’ll try adjusting the TVC cable and report back on results. Thanks for the input!

Anonymous 2016-04-27 15:38

Did you use ATF4 transmission fluid? Avoid Dexron or universal fluids—only ATF4 is compatible with the 42RE.

Anonymous 2016-04-27 15:46

Yes, we used ATF4. The shifting problems were already present before replacing the TPS, so it's unlikely that the TPS was the root cause.