O2 sensor code 21 - DodgeForum.com

Go Back  DodgeForum.com > Dodge Trucks > Dodge Ram > 2nd Gen Ram Tech
Reload this Page > O2 sensor code 21
Notices
2nd Gen Ram Tech 1994-2001 Rams: This section is for TECHNICAL discussions only, that involve the 1994 through 2001 Rams. For any non-tech discussions, please direct your attention to the "General discussion/NON-tech" sub sections.

O2 sensor code 21

Reply

 
 
  #1  
Old 07-13-2017, 02:16 PM
CJSuhr's Avatar
CJSuhr
CJSuhr is offline
Veteran
Thread Starter
Join Date: Nov 2016
Location: Omaha NE
Posts: 252
Default O2 sensor code 21

So as many of you know I did a automatic to 5spd swap in my 94 360. Everything went together well, but I've been having trouble with my PCM communication with my O2 sensor. I noticed this problem when I was running my 360 with the 318 manual pcm I removed from my parts truck, before I oredered a 5.9 manual pcm. The fist thing I did was change my o2 sensor out with a brand new denso unit, thinking my origional o2 finally died. Same issue. Once the pcm grounds the ASD relay to send itself into closed loop one the truck is warmed up the CEL illuminates. Now I've gone ahead and tested my harness for continuity.

Pin 2 on o2 side to pin 41 pcm side is the sensor signal, it reads good.

Pin 1 o2 side to pin 4 pcm is sensor ground, that checks out.

12v to asd relay checks out

ASD to pin 4 o2 checks out

Pin 57 Pcm to control side of ASD relay checks out

The harness I have is a 95 from a 5.2 half ton, which means it is wired only for a single O2 sensor. But the cel still illuminated with the 5.2 pcm.

Now since I'm usi a 5.9 HD pcm, does it call for 2 O2 sensors like all the FSM's state? Nowhere else on the internet have I found that the 94-95 HD 5.9 and 5.2 trucks have 2 o2 sensors, one in each bank. It seems like that's only on the v10? Or do all HD federal emision trucks have 2 pre cat o2 sensors?

Even so, if that's the problem with my 5.9 HD pcm, that doesn't explain why I had the same code 21 with my 5.2 half ton pcm.

Anyone who can confirm that the 94-95 5.9 gas 2500-3500 trucks have 1 or 2 pre cat o2 sensors please let me know.
 
Reply With Quote
  #2  
Old 07-13-2017, 02:22 PM
CJSuhr's Avatar
CJSuhr
CJSuhr is offline
Veteran
Thread Starter
Join Date: Nov 2016
Location: Omaha NE
Posts: 252
Default

O2 sensor code 21-image.jpg
 
Reply With Quote
  #3  
Old 07-13-2017, 02:25 PM
HeyYou's Avatar
HeyYou
HeyYou is online now
Super Moderator
Join Date: Apr 2010
Location: Clayton MI
Posts: 43,399
Default

I know the HD engines had some differences, they should be detailed, sorta... in the FSM.

The Code 21 indicates the sensor is shorted to voltage, OR, stays at center..... Do you have a scanner that will let you read data, and see what the sensor is actually doing?
 
Reply With Quote
  #4  
Old 07-13-2017, 02:26 PM
HeyYou's Avatar
HeyYou
HeyYou is online now
Super Moderator
Join Date: Apr 2010
Location: Clayton MI
Posts: 43,399
Default

There should be a separate entry for the HD version of the engine in the wiring diagrams.
 
Reply With Quote
  #5  
Old 07-13-2017, 02:28 PM
CJSuhr's Avatar
CJSuhr
CJSuhr is offline
Veteran
Thread Starter
Join Date: Nov 2016
Location: Omaha NE
Posts: 252
Default

O2 sensor code 21-image.jpg
 
Reply With Quote
  #6  
Old 07-13-2017, 02:30 PM
CJSuhr's Avatar
CJSuhr
CJSuhr is offline
Veteran
Thread Starter
Join Date: Nov 2016
Location: Omaha NE
Posts: 252
Default

Originally Posted by HeyYou View Post
There should be a separate entry for the HD version of the engine in the wiring diagrams.
I do not have a scanner that can read the data. That is the only v8 entry in the 95 FSM. The other two are the v6 which shows only one sensor and the v10 with is basically the same thing as the v8 drawings.
 
Reply With Quote
  #7  
Old 07-13-2017, 02:42 PM
HeyYou's Avatar
HeyYou
HeyYou is online now
Super Moderator
Join Date: Apr 2010
Location: Clayton MI
Posts: 43,399
Default

Ok, check out this page for some troubleshooting tips. Unfortunately, OBDI doesn't specify WHICH sensor is causing the trouble, if there is more than one.

Also, it appears that the HD PCM IS going to expect a left, and right, O2 sensor. Looks like the left side one goes to pin 23 in the PCM connector. Is there anything there?
 
Reply With Quote
  #8  
Old 07-13-2017, 02:47 PM
CJSuhr's Avatar
CJSuhr
CJSuhr is offline
Veteran
Thread Starter
Join Date: Nov 2016
Location: Omaha NE
Posts: 252
Default

Originally Posted by HeyYou View Post
Ok, check out this page for some troubleshooting tips. Unfortunately, OBDI doesn't specify WHICH sensor is causing the trouble, if there is more than one.

Also, it appears that the HD PCM IS going to expect a left, and right, O2 sensor. Looks like the left side one goes to pin 23 in the PCM connector. Is there anything there?
There isn't nothing for the left o2 sensor as i am using the 5.2 manual 1/2 ton harness. I just wasn't for sure or not whether the HD version of the V8 had a second one, because I could not find info on that anywhere else online except for the service manual.
 
Reply With Quote
  #9  
Old 07-13-2017, 02:53 PM
HeyYou's Avatar
HeyYou
HeyYou is online now
Super Moderator
Join Date: Apr 2010
Location: Clayton MI
Posts: 43,399
Default

In the 94 manual, section 14-32, figure 2 shows a wiring diagram for the HD PCM, and clearly shows two O2 sensors. (left and right)

I can't find any info on whether or not dodge has any additional codes for the HD engines. (which would have been nice.)

If there isn't a wire for the left side O2 sensor, I suspect you could fool the pcm, simply by feeding the signal from the one that is there, to both pins....... Would it solve your problem? That, I don't know.
 
Reply With Quote
  #10  
Old 07-15-2017, 07:25 AM
Moparite's Avatar
Moparite
Moparite is offline
Record Breaker
Join Date: Feb 2015
Posts: 2,062
Default

I found that the 94-95 HD 5.9 and 5.2 trucks have 2 o2 sensors
Was there a HD 5.2 in 94-5? According to my 96 fsm it was only the 5.9 that was HD. Not sure if the vin sequence is the same but the 8th digit is for the engine. Z is the standard and 5 is HD. If you swapped in HD pcm you will need the harness for it also due to the extra 02.
 
Reply With Quote
 
 
 


Thread Tools
Search this Thread
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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump

Featured Sponsors

All times are GMT -4. The time now is 12:47 PM.