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Old 12-30-2016, 09:15 PM   #1
n8thgr8
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Default sorting out o2 sensors

So I've been having problems with my o2 sensors for years, and I'm finally figuring out what is going on with them. It would appear that there isn't any voltage, and only 1 of the 4 sensors is reading.
SO, now that I have THAT critical bit of information, my question for you guys is this...
What next?
Has anyone experienced this before? (I mean, of course they have! this is Dweb!)
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Old 12-30-2016, 11:06 PM   #2
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Default Re: sorting out o2 sensors

No voltage? What codes do you have ? You have 4 wires going to each sensor. The heater is only going to have battery voltage during warm up. The signal wire has about 1/2 a volt till the o 2 sensor starts making about a volt to ride on top of that 1/2 volt. Each one of those signal wires is a different color. But each sensor has a red/ black wire that is a ground when the engine is running. My money is on that set of red / black wires have no ground thru the PCM. Post up what you find when you measure the voltage at those wires.
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Old 12-30-2016, 11:13 PM   #3
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Default Re: sorting out o2 sensors

I would try to get a t pin or something back probed into one of the red/black wires and ground it with a jumper wire. Then see if you get activity on that sensor. Rear one will be easiest for sure.
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Old 01-01-2017, 11:37 PM   #4
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Default Re: sorting out o2 sensors

Ah. I'll have to admit that when it comes to electrical problems I'm not very good at them.
FOr a long time I've had P1187, a bank 1 problem. But at the time my scanner was so basic I didn't have any other information. But the symptom is horrific gas millage. mixing WAY too rich.
I have since gotten a wifi OBDII reader and the apps I use are a lot more comprehensive. (dash command and OBD car doctor)
What they tell me is that only 1 of the 4 O2 sensors is reading, and that the voltage for the rest is zero.
I think what I'm going to do, I have to bring the truck to the shop to finish up my ABS nightmare (modulator) and I'll have them take a look at it.
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Old 01-02-2017, 11:53 AM   #5
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Default Re: sorting out o2 sensors

I think I thought you were working on a Disco 2 .Non of what I said applies to a Disco 1.
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Old 01-02-2017, 10:57 PM   #6
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Default Re: sorting out o2 sensors

haha, that only partly explains why it made no sense to me. I appreciate your help though.
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Old 01-03-2017, 09:29 AM   #7
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Default Re: sorting out o2 sensors

Only 1 of 4 O2 sensors is sending a reading and you don't have any codes? ...or only 1 code? That doesn't sound right.

If you need to replace the sensors, these appear to be the cheapest/best replacements...
https://www.amazon.com/dp/B001PNG622...I33ZROE0N6JEK4
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Old 01-03-2017, 03:48 PM   #8
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Default Re: sorting out o2 sensors

Quote:
Originally Posted by WaltNYC View Post
Only 1 of 4 O2 sensors is sending a reading and you don't have any codes? ...or only 1 code? That doesn't sound right.

If you need to replace the sensors, these appear to be the cheapest/best replacements...
https://www.amazon.com/dp/B001PNG622...I33ZROE0N6JEK4
Walt would these also be the same for a 1996 GEMS? I need to put in two new sensors, too.
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Old 01-03-2017, 04:00 PM   #9
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Default Re: sorting out o2 sensors

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Originally Posted by AbnMike View Post
Walt would these also be the same for a 1996 GEMS? I need to put in two new sensors, too.
I have used these NGK/NTK sensors on my D1 with good results. I would buy them again.
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Old 01-03-2017, 04:03 PM   #10
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Default Re: sorting out o2 sensors

Quote:
Originally Posted by Tugela View Post
I have used these NGK/NTK sensors on my D1 with good results. I would buy them again.


Are you AEL or non-AEL? I'm non AEL.

(Not even sure if it matters but figured I'd mention it).


Thanks.
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Old 01-03-2017, 04:08 PM   #11
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Default Re: sorting out o2 sensors

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Originally Posted by AbnMike View Post
Walt would these also be the same for a 1996 GEMS? I need to put in two new sensors, too.
I believe your 1996 (pre-AEL) will have a different connector than the AEL truck in the original post.

This thread might be helpful.....
https://discoweb.org/forums/showthre...or#post1032507
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Old 01-06-2017, 07:28 PM   #12
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Default Re: sorting out o2 sensors

Jesus H. Christ at replacing these things.

Glad someone posted about removing the coil pack and laying on the motor. Even then undoing the clips took forever.
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Old 01-08-2017, 04:37 AM   #13
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Default Re: sorting out o2 sensors

You must have to do that with at D2 as well. Replacing the sensors in a D1 is mostly a snap. The ones that are in front of the Cats are a little tricky, but just reaching behind the engine and with a little dexterity you can snap the new sensor into the plug.
All my sensors are brand new, I have the correct ones for my AEL system.
What I'm thinking is that there is something wrong between the pigtail plug and the ECU.
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Old 01-08-2017, 01:40 PM   #14
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Default Re: sorting out o2 sensors

I've always found unthreading the O2's from the bungs to be the hardest part. More times than not I've had to drop the entire Ypipe, cut the wire on the bad O2, and use a deep 6 point socket and impact gun to get it out.
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Old 01-25-2017, 07:08 PM   #15
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Default Re: sorting out o2 sensors

I've been rooting around with my o2 sensors, and I've discovered that there are several loose connections with wires into the connector plug.
Is there such thing as a replacement plug on the ECU side?
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Old 04-19-2017, 11:10 AM   #16
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Default Re: sorting out o2 sensors

Quote:
Originally Posted by n8thgr8 View Post
I've been rooting around with my o2 sensors, and I've discovered that there are several loose connections with wires into the connector plug.
Is there such thing as a replacement plug on the ECU side?
I haven't seen replacements but have performed the replacement with a used plug.
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Old 05-20-2017, 01:53 PM   #17
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Default Re: sorting out o2 sensors

Quote:
Originally Posted by n8thgr8 View Post
You must have to do that with at D2 as well. Replacing the sensors in a D1 is mostly a snap. The ones that are in front of the Cats are a little tricky, but just reaching behind the engine and with a little dexterity you can snap the new sensor into the plug.
All my sensors are brand new, I have the correct ones for my AEL system.
What I'm thinking is that there is something wrong between the pigtail plug and the ECU.
I am seeing a similar problem. I just put two new 25044 sensors on bank 1. Sensor 1 still shows 1V straight across. Sensor 2 shows 0V straight across.

Ugh.
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Old 05-20-2017, 07:55 PM   #18
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Default Re: sorting out o2 sensors

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Originally Posted by Injuhneer View Post
I am seeing a similar problem. I just put two new 25044 sensors on bank 1. Sensor 1 still shows 1V straight across. Sensor 2 shows 0V straight across.

Ugh.
It turns out that the ground for the bank 1 sensors in the ECU is not providing a zero reference.

When I checked the signal for each sensor at the ECU the bank 1 signals were at +1.0V. Bank 2 signals were at 0V. A second check of the bank 1 signals showed one at +1.0V->+1.99V and other at 0V.

It seems the reference for the bank 1 signals is wrong. I tied the ground for the front sensors together to bring the ground reference down and suddenly the bank 1 front started working. I am assuming that the ECU couldn't read the voltage above 1.0V.

When probing the bank1 rear sensor I found a similar problem. Tieing the ground from bank 2 to bank 1 started the bank 1 rear working.

So the wiring is fine. The problem appears to be inside the ECU.

Now I am wondering if the persistent high idle problem my truck is experiencing is due to an incorrect voltage reference.
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Last edited by Injuhneer; 05-21-2017 at 01:03 AM.
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Old 05-21-2017, 03:26 PM   #19
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Default Re: sorting out o2 sensors

Quote:
Originally Posted by Injuhneer View Post
I am seeing a similar problem. I just put two new 25044 sensors on bank 1. Sensor 1 still shows 1V straight across. Sensor 2 shows 0V straight across.

Ugh.



Did you say that you put the same part number sensors on the same bank? There is a "front" sensor, and a "rear" sensor for each bank. There has to be a reason for "front" and "rear" sensors. Could this be the reason for your readings being the way they are?
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Old 05-21-2017, 08:20 PM   #20
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Default Re: sorting out o2 sensors

Every reference I could find for a '97 D1 pre AELS uses the same sensor at all positions.

Part of my procedure was to swap the known working sensors from bank 2 to bank 1 (and new from ban 1 to bank 2) with no change in behavior. The sensors were swapped back with no change. The new sensors did BTW work on bank 2.

Sorry if that wasn't clear.

BTW - I was able to move the pins from the new connector of the 25044 to the old plugs. No splices.
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