EGR Temp Sensor Diagnostics

[Buck Bridges]

1995 EGR Temp Sensor Problems...

Hey wonderful people...

First of all, thank you to all the folks who share their time and experience to help us keep the 4runners on the road. I bought my 1995 3.0 2WD (150k miles) a couple of months ago and this forum has really been an awesome resource. Again, thank you all!!

Ok, here is the rundown. Bought the truck and suspected it had a burnt valve as the compression test showed 50psi in Cylinder 1. There was a bit of an oil leak coming from the valve cover so pulled off the head to check the valve and replace the valve cover gaskets. Valves were fine and did a bit more snooping around and then I found it... A RAT had made its home in the engine compartment and it had chewed through the fuel injection wires! That was a quick fix, and problem solved. Compression was back to normal and all is good...

Drive about 50 miles and the CEL comes on. I had noticed it was a bit sluggish but I just assumed thats the way it drives. Code 71, "EGR System Malfunction" and then I do a few things to check my system,

1) Checked the EGR Valve and did the vacuum test and the engine stalled like it should. EGR Valve is working properly.

2) Took apart the Vacuum Modulator and cleaned the filter. No problems

3) Checked all the hoses for cracks and leaks but everything looks good.

4) Double checked the vacuum hose diagram to make sure all the hoses are connected properly. Since I took off the head, it is very possible that I didn't connect it all correctly. To the best of my knowledge, everything seems to be in the right spot.

5) Took it in the shop! I read a post on this forum that said, "Hey, after you've done all you can do, stop wasting the time and money and get a professional to look at it!" I took that advice.

They said my EGR Temperature Sensor was the culprit and quoted me $300 for the new sensor. WHAT?!? I found one online for $140 but I haven't ordered it yet because I am still not convinced that is the source of the problem. Pictures are attached.

My questions...

1) Is there any way to test the temp sensor to verify that is the cause of the problem? I can't find much in the manual.

2) If you look at the picture closely, you can see a little bit of damage to the sensor wires. It is reasonable to think that is whats causing the malfunction?

3) The temp sensor is connected to two wires, one green and one brown/reddish. Does it matter how they are connected to the temp sensor? Meaning should green be on the left plug or vice versa?

4) Are the green and brown/reddish wires grounded correctly? In the picture, you can see that the copper wire is actually not connected very well. Would you suspect that might be causing the temp sensor error?

Thank you for taking the time to share your thoughts. If the solution is to buy a new EGR temp sensor than that's what I'll do but I want to find a way to determine if that is the actual cause of the problem. Any and all suggestions are greatly welcomed!

 

[willyt4r]

10k resistor

place a 10 k resistor across the connection and your problem will go away. Cost is $1.08 from radio shack. A search for 10k resistor will provide a wealth of information.

 

[Blueaussie]

Buck and Willy

I may have the same problem. Buck my plastic connector broke and I to put wire terms on like you but the wires on mine or not color coded so I am unsure if I even have it connected correctly. If I do not would this cause the engine check light to come on.

Thanks for the post and pictures Buck, I love this forum!

 

[Buck Bridges]

Thanks for the tip Willy. I've done a bit of reading on the 10k resistor but I do have a couple of questions. It seems this only a way to bypass the sensor and so it won't "fix" the problem. I understand that the CEL should go away but is this an actual solution to the horrible MPG and sluggishness that the truck has?

 

[Buck Bridges]

I may have the same problem. Buck my plastic connector broke and I to put wire terms on like you but the wires on mine or not color coded so I am unsure if I even have it connected correctly. If I do not would this cause the engine check light to come on.

Thanks for the post and pictures Buck, I love this forum!

Thats a good question Blue... I was wondering the same thing myself. I plugged it in and drove around for a few miles then I switched the plugs to see if there was any difference and I didn't notice any improvement.

I would love a picture of someone's temp sensor w/ resistor or even the factory installed to see if my wire connections are right. I can't find this info in the manual.

 

[Buck Bridges]

Bump... Bump

 

[bills86e]

Buck, Ya need to seal those terminals so moisture doesn't get to the crimp.
I reckomend solder and marine heat shrink terminals. Under hood gets alot of moisture, and the electricals produce four times the corrosion when electrically active. Marine type had a glue that seals when the shrink tube is heated.

Bills86e

 

[Buck Bridges]

Hey Bills... Thanks for the suggestion. I will keep that in mind once I have the my problem fixed.

 

[Buck Bridges]

Update...

I've already ordered a new EGR Temp Sensor and it should arrive in a couple of days. I went on and bought the 10k (1/4 Watt) resistor at Radio Shack to plug into the old sensor. My thinking is that if the old Temp Sensor is still functional and I still have CEL after a few days, I will know that the Temp Sensor isn't the problem however when I checked for resistance, I got nothing... It just stayed at "1" while in the 20k setting. It seemed putting in a resistor would be a better test of the Temp Sensor than doing a hot oil test. Does anyone think my logic is incorrect?

I added pictures below in case anyone wants to see the 10k resistor plugged into the Temp Sensor. I didn't solder as this is just a test and it will only be used to determine if the sensor is working at all. Will this do the trick... I wonder

 

[Buck Bridges]

What is this?!?

Still going through my vacuum hoses and I'm having a tough time finding a diagram that shows ALL the hoses. Hope someone can help me out. Excuse the crude drawings but its the only way I can show the lines I have.

First of all, can anyone please tell me what that part is that I have circled in red? As you can see from the diagram I've attached, this part isn't included however, I have vacuum lines running to and from this part. Assuming its a (grey) VSV but what is it next to? Are those fuel lines

You can also see in the top left of the picture that has the 3 prong plastic piece with one cap and two vacuum hoses. Quick question, is that check valve supposed to pass air through it by blowing or sucking, (thats what she said) as I wasn't able to get any air through it. Also, I've seen some pictures of the 3 prong plastic piece have 2 hoses coming from it. Any known reason why I have one plugged?

Another question... (I'm sure there is a name for it but I'm gonna keep calling it the 3 pronger) The 3 pronger has one hose going to the (AS) with the check valve and if you look at the other hose, it is split into a "T" one hose going to the mysterious red circled part and the other going to the (FPU.) The diagram doesn't show that.

Lastly, I have included the diagram with a crude line drawing of my vacuum routing. Here is a quick rundown,


Blue Line - With check valve from 3 pronger to back port of (AS)

Green Line - AS Reed Valve to inside port of (AS)

Red Line - 3 Pronger to VSV and it "T's" to the back of (FPU)

Purple Line - Far left of the 3 metal tubes at base of EGR Valve to front of (FPU)

Brown Line - Far right of the 3 metal tubes at base of EGR Valve to front of (EGR)

Pink Line - Middle of the 3 metal tubes at base of EGR Valve to back of (EGR)


Sorry for the long winded post but if this is correct, I wanted to include pictures and specific routing for others with this same problem. I've spent the past week scouring over every EGR post on all the forums and there isn't much more than the same old diagram. Thank you for your help!! Hope this helps someone else too

 

[2ndGen4runner4x4]

You do realize that the 10k resistor needs to be connected across (between) the wires back to the ECM right?
Also... it doesn't matter which way those 2 wires are hooked up to the EGR temp sensor. It's just a temperature resistor in the circuit.

The 3.slo is not known for great power or gas mileage. What are you trying to accomplish? Just trying to get rid of the CE light?

 

[Buck Bridges]

You do realize that the 10k resistor needs to be connected across (between) the wires back to the ECM right?
Also... it doesn't matter which way those 2 wires are hooked up to the EGR temp sensor. It's just a temperature resistor in the circuit.

The 3.slo is not known for great power or gas mileage. What are you trying to accomplish? Just trying to get rid of the CE light?

All those years in High School taking French when I should have been taking an electronic class. Well, goes to show that a dummy with a pack of resistors isn't getting very far :trophy:

I was trying to diagnose my EGR system. The shop told me the temp sensor needed to be replaced and I got the tip about the resistors. Thought I'd give it a try to see if that removed the CEL. Even if it did and I hadn't screwed up the simple task of connecting the resistors, I was/am still planning on finding the problem and fixing it.

Got the new temp sensor today and I've noticed a serious difference in the performance. Its still a bit sluggish but I'm waiting to see if the light comes back on. Fingers crossed

 

[bills86e]

Buck, Buy some CRC throttle body cleaner, clean the idle air controller valve and throttle body. I'd bet that improves its performance!

 

[Buck Bridges]

Buck, Buy some CRC throttle body cleaner, clean the idle air controller valve and throttle body. I'd bet that improves its performance!

I checked the throttle body and looked inside... It was surprisingly clean for an engine with 150k miles. There was almost zero carbon buildup so I decided to leave it. I was hoping to find it dirty as that would have been a quick fix to improve performance but darn... I didn't remove the idle air controller as I assumed it would be clean as well. I wonder what could be causing the sluggishness now that the EGR system is operational again.

Back to the drawing boards again Thank you for the tip Bills

 

[2ndGen4runner4x4]

I wonder what could be causing the sluggishness now that the EGR system is operational again.

I think I saw yours on Austin craigslist a while back?
Has it ever been non sluggish to you? 3.slo's with automatics are notoriously underpowered.
Try driving it while manually shifting the tranny. That's what I do... around town, I mostly leave it in 2nd gear.

 

[Buck Bridges]

I think I saw yours on Austin craigslist a while back?
Has it ever been non sluggish to you? 3.slo's with automatics are notoriously underpowered.
Try driving it while manually shifting the tranny. That's what I do... around town, I mostly leave it in 2nd gear.

Yeah, got it off of Austin Craigslist. A rat had chewed through some fuel injector lines. Was concerned it something worse at first so far it has worked out.

Since I've had it, it has always been a bit sluggish but it could very well just drive that way. Although, a guy from a shop said it a bit sluggish too when he drove it so I'm not sure. Just a couple of hours ago, my battery arced when trying to start it. Shot up a good 6 inches without being touched. Just happened to have the hood up. Fix one thing and another pops up... Good times

 

[Buck Bridges]

Update...

Replaced the EGR Temp Sensor and CEL has not returned. Replaced all the vacuum lines just because it was easy and only cost 6 bucks for all the lines. Thank you all for the suggestions. Hope this helps someone down the road