P0132 and P0138 Diagnostic Issues on 2004 Chrysler Pacifica AWD with Aftermarket Catalytic Converter

I forgot to mention that the Check Engine Light was not illuminated before installing the aftermarket catalytic converter. After replacement, the light became active and persistent. This suggests a direct link between the exhaust system modification and the OBD2 fault codes.

I believe you have two primary issues: first, the aftermarket or universal catalytic converter does not meet OEM specifications and fails to properly process exhaust gases. Second, Bosch oxygen sensors are not designed for Chrysler vehicles and often fail due to incorrect heater resistance — they do not reach operating temperature quickly enough to provide accurate feedback to the PCM.

Agreed! A high-quality direct-fit catalytic converter is essential. Walker models (e.g., 93268) are reliable and use the same substrate design as their CARB-certified versions, offering better performance than generic universal converters. Regarding O2 sensors, Bosch units are not OEM-spec compliant — especially on Chrysler platforms. NTK sensors are recommended for proper heater resistance and response. I suggest removing Bosch sensors entirely and installing correct NTK parts. Also check for exhaust leaks or EGR valve issues, as fuel smell may indicate a leak. What brand of catalytic converter did you install originally?

I used a MagnaFlow 94000 series catalytic converter. Are universal converters inherently flawed due to insufficient substrate material? If so, would the Walker 93268 (described as universal) have sufficient substrate and match OEM design? Regarding O2 sensors — are Bosch units truly not compatible with Chrysler systems? I spoke with a local dealership, which confirmed no known issues with Bosch O2s in general but noted that Bosch spark plugs are problematic on Chryslers. They recommended NTK oxygen sensors. Are there any other brands you'd suggest as alternatives? Given my budget constraints after spending heavily on a new PCM and other parts, what would be the best path forward? Option 1: Replace catalytic converter (cost ~$100) to see if codes resolve. Option 2: Install NTK O2 sensors and splice post-cat sensor (cost ~$114). My main question: Can a faulty downstream O2 sensor cause a pre-cat code like P0132? This will be key in deciding my next step.

You're spending too much due to an incorrect diagnosis. The mechanic should refund part of the PCM cost — this is not a valid repair and is widely documented on automotive forums as a misdiagnosis. Bosch O2 sensors are not OEM-compliant in design, especially for Chrysler vehicles. Most low-quality converters fail because they lack sufficient substrate or improper material mix. The best solution is a CARB-certified direct-fit catalytic converter that meets California emissions standards. These have the highest success rate in preventing P0420 codes. Before spending more on sensors, fix the root cause — start with proper O2 sensor installation and then evaluate if codes return. Also, seek a more competent repair shop for future diagnostics.

Thanks! I've spoken to several direct-fit catalytic converter manufacturers and an experienced exhaust specialist. I now understand the issue better. They emphasized that the spacing between the two O2 sensors is critical — improper positioning can trigger MIL activation. The universal cat I used lacked CARB certification, which is essential for this model due to its emissions sensitivity. While some brands (like Catco) claim their non-CARB converters use identical substrate and design as CARB-certified models, California regulations require compliance for proper emissions performance. I am replacing the front pipe and catalytic converter first, then proceed with O2 sensor installation. This allows me to test the system without further expense. It's a costly fix — but I'm learning through trial and error. Thanks again!

I've installed a new front pipe and catalytic converter, along with two new NTK O2 sensors. After disconnecting the battery to reset the system, I drove less than 100 yards — the check engine light returned, and the scan tool detected P0138. Two possible causes: (1) faulty oxygen sensor or (2) short to battery voltage in the post-cat O2 signal circuit. I’m now considering replacing the O2 sensor first before seeking a diagnostic. The issue is that I started with two codes (P0132 and P0138), which reduced to one after installing NTK sensors — this suggests Bosch units were problematic. Fuel efficiency has improved from 14–16 mpg to over 19 mpg, and there’s no visible fuel smell. The car runs smoothly with a slight drop-in acceleration. I don’t see an EGR hose issue, but could the EGR valve itself be faulty? Open to any suggestions. Thanks in advance for input.

If you drove less than 100 yards and the code returned immediately, it points strongly to a wiring or circuit issue with the O2 sensor — not necessarily a faulty part. An EGR valve malfunction would typically reduce fuel economy and cause drivability issues. Since your car runs well but still shows a code, I suspect the problem lies in the sensor harness or connections at the O2 sensor connector. Given known Pacifica wiring vulnerabilities near the PCM, this should be checked first.

Thanks for the response! So — would you recommend replacing the oxygen sensor first, or taking it to a professional diagnostic shop instead?

If you’ve installed correct NTK O2 sensors and the code returns within minutes of driving, then yes — take it in for a full diagnostic. It’s unlikely that the NTK sensor is faulty if the part number matches OEM specs. The 2004 Chrysler Pacifica has known wiring harness issues near the PCM connectors — this should be checked first. A professional scan with live data and circuit testing will help identify whether the issue lies in the sensor or its electrical connections.