EGR temp sensor tested open. Bad?

[BrettinSanAntonio]

While chasing some CEL demons, I walked through the trouble shooting process for most of the EGR system and found my EGR temp sensor to have no resistance or even continuity. It reads as an open circuit so my thought is the sensor is dead.

Has anyone run across a bad EGR temp sensor before?

 

[BrettinSanAntonio]

Anyone?

 

[NaterGator]

What are you metering with?

The EGR sensor has a very high impedance and a cheap-o meter might not read it well. Get yourself a Fluke, everything else is just a toy

 

[BrettinSanAntonio]

What are you metering with?

The EGR sensor has a very high impedance and a cheap-o meter might not read it well. Get yourself a Fluke, everything else is just a toy

One of the meters I used was a 20 year old Fluke and the other a new mid level brand.

After looking a the testing procedure again, I think my diagnosis is correct. The range of resistance according to the FSM is only 2K ohms - 97K ohms, depending on the respective temperature of the sensor.

That's hardly a wide range and should be easy to measure with the cheapest of multimeters. 97k being the upper end, really isn't that much resistance so my measurement of an open circuit should mean just that.

CDan has one on the way and we'll see what the new part measures.

 

[landtank]

found my EGR temp sensor to have no resistance or even continuity.

by definition "no resistance" is continuity. So it would either have continuity or some resistance.

 

[NaterGator]

I remember my temp sensor reading as high as 500MΩ when cold, so I dunno what to tell you.

 

[medtro]

I remember my temp sensor reading as high as 500MΩ when cold, so I dunno what to tell you.

In that case, I would say your sensor is not within specs.

 

[jasonmt]

I remember my temp sensor reading as high as 500MΩ when cold, so I dunno what to tell you.

What meter were you using that gave you a 500MΩ value?

 

[BrettinSanAntonio]

Yep, I mis typed there. What I meant was I measured the circuit as being "open" or no continuity.

by definition "no resistance" is continuity. So it would either have continuity or some resistance.

 

[BrettinSanAntonio]

Wow...500M! Hmmmm....that's really WAY out of the specs for testing set by the FSM. Was it really cold outside? At 122 degrees it should read 64K -97K.

I remember my temp sensor reading as high as 500MΩ when cold, so I dunno what to tell you.

 

[gray]

One of the meters I used was a 20 year old Fluke and the other a new mid level brand.

After looking a the testing procedure again, I think my diagnosis is correct. The range of resistance according to the FSM is only 2K ohms - 97K ohms, depending on the respective temperature of the sensor.

That's hardly a wide range and should be easy to measure with the cheapest of multimeters. 97k being the upper end, really isn't that much resistance so my measurement of an open circuit should mean just that.

CDan has one on the way and we'll see what the new part measures.

How did this turn out?

I just attempted to check my EGR temp sensor (it was hot after driving 8 miles and then racing the rpms at 4000 for three minutes per the FSM) but the ?cheap multimeter just stayed on 1 at the far left of the display; no matter what range I put the dial on it displayed
a 1 at the far left of the readout, not on the right as usual.

Then I immediately checked other components; like the harness side
of the EGR Temp sensor connector and got 5.0 volts after switching
to the volt scale.

Then I switched back to the ohm scale and checked the VSV short harness connector (in front of the intake), and got a 36 when
on the 200 setting, and .03 when on the 20K setting.

What is going on here; any ideas ?

The meter, my technique, or a bad temp sensor??

G

 

[landtank]

sounds like "1" being displayed is open. What does the meter display when set to ohms and not attached to anything?

 

[gray]

I will check it again today, was in a hurry yesterday in the rain;
but as I recall, before touching anything it displayed a 1 on the far left of the screen,
then when I checked the other components it started reading and in a couple of seconds stabilized
and showed a reading on the far right of the screen, like 5 volts, 36 ohns, but when I tried to
check the temp sensor, it just stayed on 1, but on the far left; ie: like it was reading nothing.

I will use a different multimeter today; I'm learning, slooowly.

g

 

[landtank]

I will check it again today, was in a hurry yesterday in the rain;
but as I recall, before touching anything it displayed a 1 on the far left of the screen,
then when I checked the other components it started reading and in a couple of seconds stabilized
and showed a reading on the far right of the screen, like 5 volts, 36 ohns, but when I tried to
check the temp sensor, it just stayed on 1, but on the far left; ie: like it was reading nothing.

I will use a different multimeter today; I'm learning, slooowly.

g

sounds like it;s reading an open circuit just as when the leads are touching nothing.

 

[gray]

Update;

OK, this should do it, I took my time, borrowed another multimeter.

Cold new temp sensor: 255K ohms (on 2000K setting) which is in spec
for a cold sensor.

The FSM gives slightly different numbers in two places; on EG262 it says 600K or less, open circuit will be 720K or more;

then on another page, EG 264, it gives a range for a cold EGR temp sensor;
188.6 to 439.0 K ohms at 20 C(68F)

Hot (old) temp sensor in the vehicle: 80K ohms initially after reving hot engine for 4000 rpms for 3 minutes.

I continued to watch it as I noticed it continued to go down a tenth every 2 seconds or so,
and after 10 more minutes of reving it was at 55K ohms.

I got tired after holding the throttle for 10 more minutes and stopped the test.

The FSM does not however say watch it for X number of minutes, it says check it while reving
at 4000 rpms after having already reved it as 4000 rpms for 3 minutes, with the VSV connector disconnected.

Best I can figure out is that as I continued to rev it, it got hotter, which caused the resistance
to go lower, but it never got close to the 4.3 K ohms or less for a good test.

I think this does it; I have a bad temp sensor as the FSM says it should read 4.3K ohms or less.

Anyone have anything to add? More testing?

Of course, this does not mean I have solved my P401, just that I have found that I have a bad
temp sensor.

G

 

[landtank]

I doubt it is the sensor.

 

[gray]

I doubt it is the sensor.

Landtank

You doubt my temp sensor is bad
or,
you doubt by putting in a new one, it will solve my P401 problem?

Either way; any suggestions?

g

 

[landtank]

to properly check any sensor of this type it needs to be removed from the system and checked with a reliable heat source.

the sensor passes the cold resistance check and does change with applying heat. I doubt very much that the sensor is bad. I've seen it maybe twice in 25 years of working with similar devices.

After revving the truck and not getting the ohm drop that you should it is more likely that you aren't flowing enough exhaust gases to generate the needed heat to satisfy the ECM.

The only way to absolutely know if the sensor is good is to place it in a water bath at a controlled temperature. I don't know this circuit well enough off the top of my head but I have to think that somewhere in the FSM a water bath is suggested to evaluate the sensor's condition. This is standard diagnostic procedure.

 

[gray]

I followed the test procedure in the FSM; pages noted in my post;
no mention in the FSM of using a hot water test for the EGR temp sensor.

However, it does follow logically that it could be tested by that method, but there are no temp specs given for this EGR temp sensor.

ie: the FSM does not say; " test at XX degrees for three minutes---"

It tells you to check in the vehicle, sensor connector disconnected, with the engine warm after racing at 4000 rpm for three minutes, then checking it also while racing the engine,
and also while the VSV is disconnected.

So, with the VSV disconnected, which happens; more, or less opening of the EGR??

As I mentioned above; the ohms continued to fall slowly the longer
I held the rpms up; but very slowly; like over 10 minutes additional
testing time beyond what the FSM calls for, however, it never reached the 4.3k ohm cut-off for a good sensor.

G

 

[gray]

ps;
I did not check the in-vehicle sensor cold;
the cold test was of the new sensor which I have not installed yet.

If anyone can show me where to find the alternate test method and at what temp
to test it at, please let me know.

thanks
g