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Discussion Starter #1
Greetings,

I took my '94 Tracker in for a smog check to renew the registration.
The tech. said that the rig passed all the emissions tests, but he could not issue a smog cert. because he didn't get a signal from the egr.

I'm not sure where to start with this issue.
Does the vehicle need to be up on jack stands with the wheels spinning forward in 2wd for the egr to send a signal? The tech. did state that he took it for a drive to check if it produced a signal when driving, and stated it did not.
Any tips on where to start looking?

Cheers
 

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Do you have a probe with an electrical connection on the EGR valve?
 

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Discussion Starter #3
Do you have a probe with an electrical connection on the EGR valve?
Yes, the egr has the temp. probe.

I have not tested resistance on it...that's an easy test...
Do you happen to know the resistance range for a correctly operating probe?

Cheers
 

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Regarding the resistance, as the probe is actually a thermistor, it’s according to temperature. The range is approximately 215+ ohms at 68F to about 11 ohms at 176F.
You may also want to check the wiring - the gray/yellow wire, as well as the red/green coming out of the ECU with the 5v reference (will vary a bit according to temp).
 

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Discussion Starter #5
Thanks for the reply.

I took a temp. reading and the egr valve was 122 degrees F.
The resistance on the probe was 0.05 ohm.

This looks to be out of spec.
Can I safely assume that this part is not operating correctly?

I will trace the wiring to be sure it is not compromised.

Cheers
 

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Thanks for the reply.

I took a temp. reading and the egr valve was 122 degrees F.
The resistance on the probe was 0.05 ohm.

This looks to be out of spec.
Can I safely assume that this part is not operating correctly?

I will trace the wiring to be sure it is not compromised.

Cheers
was the wire disconnected when you got that reading? thermistor is def out of spec, should be about 25 ohms give or take at that temp so its shot if thats the case. Replace it and hopefully it should solve your issues.
 

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Discussion Starter #8 (Edited)
Thanks for the reply.
Yes, I disconnected the probe. Then tested the resistance on the probe's leads.

I just did a search for the new part and one site has it for about two hundred bucks. Wow, that's pricey! Anyone out there have a parts car they want to pull one off and sell me?

Thanks again,
Cheers
 

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I see the fault is "No signal from egr", how do we know the temperature is the missing signal ? What else gives an egr signal ? These commonly only use a vacuum valve to control the egr so only the 2 coil wires. Just thinking out loud really, I just thought egr temperature would be a more specific code but maybe not on a 1994.
 

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I see the fault is "No signal from egr", how do we know the temperature is the missing signal ? What else gives an egr signal ? These commonly only use a vacuum valve to control the egr so only the 2 coil wires. Just thinking out loud really, I just thought egr temperature would be a more specific code but maybe not on a 1994.
I thought the EGR system was pretty basic on those and relied on the temp signal to determine when it was hot enough to opent he valve. I don't think they had codes for specific parts of the control system back then.
The "missing" EGR signal from the smog test would be because the ECU hadn't seen the temp change and hadn't commanded the EGR solenoid to open I believe. Isn't this the signal they look for doing smogs? the EGR being commanded to open?(i.e. solenoid getting power). Temp thermistor would certainly stop that from happening.
 

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Thanks, I just wondered as I think Im correct in saying it was only the Californian model that has that temperature sensor. Wonder how the other older ones work, dam smog test :unsure:
 

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Discussion Starter #12
Thanks for all of the replies.

I plan on refreshing the vacuum lines while I'm in there for good measure, as well as giving the system a good cleaning.

Cheers
 

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AFAIK, The ECU has a default matrix for the EGR, based on engine temp, wheel speed and another sensor ??

The temp probe (Cal model) is the feed back that confirms EGR has operated... (gets hot with EGR flow)

The non Cal models (non thermister) use the change in O2/fuel trim to verify..

Disclaimer: at my age, memory is shady at best...😜
 

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Earlier than 1994, only the California model had the EGR probe. In 1994, through, I believe, 1995, even federal cars were lucky enough to have this wonderful item. I believe that without the thermistor, on these OBD1 models, you will not throw a code 51. My 1991 FSM indicates that the code 51 is for California models only, with the thermistor. So, lucky for me, I can ride around forever with a completely dead EGR, and no one (including myself) is the wiser.
 

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Discussion Starter #15
Thanks again for everyone's input!

One thing I'm still curious about is the actual smog check...
Does the tech. need to put the rig up on jack stands and run the vehicle in gear to get a signal from the egr?

Cheers
 

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To be honest, I have no idea how the tech would ascertain he wasn’t getting a ‘signal from the EGR’. You advise that he took it for a drive - unless he had the car hooked up to a Tech 1 diagnostic connector (which is extremely unlikely) he wouldn’t know that the EGR wasn’t working properly, without checking the emissions coming out of your exhaust. Fro OBD2 cars, they would just hook into the computer (and not need to drive the car, AFAIK). But it’s unlikely that the tech had the ability to hook into yours.
By the way, is your check engine light on when the car is running? If you actually have no signal coming out of the EGR thermoprobe, your car should throw the code 51...?????
 

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Discussion Starter #17
The check engine light did come on, however, it then went off again while daily driving.
I checked the code by jumping the connector/plug with a paper clip and got a code 51.

All of the emissions reading we within spec., just no signal from the egr.
I was scratching my head wondering how the emissions were within spec. if the egr thermistor wasn't working.

I did order the part from Rock Auto...just hoping to get this to pass inspection.

Cheers
 

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The emissions can be in spec, even without a valid EGR signal (that is the report back), remember you have OBDI
 

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Discussion Starter #19
Thanks...I'll report back after the part has arrived and is installed, and I've gotten it back from the smog. tech.

Cheers
 

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Discussion Starter #20
The Tracker passed its smog inspection with flying colors yesterday!
The new egg temp. sensor was the culprit. I could have removed and installed the part with the egr valve in place, but decided to remove the valve and give it a good cleaning. Installed a new gasket during assembly.

Thanks y'all for the help.
Cheers
 
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