NAXJA Forums -::- North American XJ Association  

Go Back   NAXJA Forums -::- North American XJ Association > NAXJA Unibody Jeep Technical Forums > Jeep Cherokee XJ (1984 - 2001) > OEM Tech Discussion
HOME Member FAQ Sponsor Info Rules Bylaws E-Mail

OEM Tech Discussion Forum for OEM (Original Equipment) or stock XJs and MJs.

Thread Tools Display Modes
Old December 2nd, 2017, 15:11
Ecomike's Avatar
Ecomike Ecomike is offline
NAXJA# 2091
Join Date: Dec 2006
Location: MilkyWay Galaxy
Posts: 14,990
Cat Converter Temp sensed in 4 wire O2 sensors!!

While using my Snap-On MT-2500 tool on my 2001 Saturn today, I made a cool discovery.

The scanner reports the actual Cat Converter operating temp!!!

Only one way that is possible folks!!! In 1987, Renix the O2 sensors had only 3 wires!!! IN 1991 OBD-1 switched to 4 wires (I think) and in 96 all OBD-II rigs I have ever seen have 4 wires. The 4 th wire is a second ground

I have always been puzzled about that second ground.

Now I know!!!

The second ground is dedicated to the electric heater in the O2 sensors.

That way the ECU/PCM can monitor the current going through heater (via the ground wire, grounding through the ECU circuit I think, noise free) and the current is proportional to the Cat Temperature!!!!

It turns the heater wire into a dual purpose gadget, called an anemometer folks!!!

Today I was sitting there watching the Cat Converter temp live on this Snap-on tool!!!

It was running at 585 F at idle and shoots up 650 F when I gun it in park for about 10 seconds. Great way to see if a Cat is dead or not, no doubt that is part of how OCD-II knows to throw a bad Cat Converter code folks!!!

These old MT-2500 scanners that cover 1984-2001 are dirt cheap on ebay now as the shops are dumping them to upgrade. Great way to help diagnose failed emissions
especially in Ca. You can watch the CPS, TPS, MAP IAT, IAC, O2 sensors, data all live with these, and so much more. Even the missfires per cyl data and spark voltage data.... and so on, find stuff long before a code is thrown.
Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091

Last edited by Ecomike; December 2nd, 2017 at 15:16.
Reply With Quote
Old December 2nd, 2017, 19:22
lawsoncl lawsoncl is offline
NAXJA Forum User
Join Date: Jan 2006
Location: North Idaho
Posts: 4,641
Re: Cat Converter Temp sensed in 4 wire O2 sensors!!

The heater current can indicate the temp of the O2 sensor, which can tell the ECM if it's hot enough to switch to closed loop mode. If it's a wide-band sensor, it can use the temp to do some calibration of the sensor. That sensor is also probably upstream of the cat. :}
Reply With Quote

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Coolant temp sensors wasillashack OEM Tech Discussion 4 April 16th, 2017 21:00
XJ overhead console grey 97+ with wire & sensors $150 SD dirtweazle SoCal For Sale 4 March 8th, 2015 08:27
WTB/ 99 XJ Converter and 02 sensors SOUTHTEXASXJ Wanted: Private Party Only 1 February 18th, 2008 12:11
Auxiliary Fan + Cooling Temp Sensors bchulett OEM Tech Discussion 11 March 10th, 2007 12:22
is there a way to wire in a torque converter lock switch for a aw4 brianb2247 Modified Tech Discussion 3 May 10th, 2006 15:36

All times are GMT -7. The time now is 08:08.

Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
NAXJA and NAXJA logo's Copyright NAXJA. All content/images Copyright NAXJA 1999-2014