Disable the EGR system the (mostly) Toyota way

[alaskacruiser]

I have no way to measure the temp of the egr. what can I use? how do I do it?

I drive my 80 everyday!! I drive it about 10 min at 80 km/hour, and a few minutes before and after at 50Km/hour. I have driven this everyday for about a week and a half with no CEL. Does any of this help?

kup99- no prob. I wasn't asking you to measure the EGR temp anyway. I was just stating that the resistor you are using (4.7kohm) corresponds to an EGR temp sensor temperature of about 280F.

As for your current setup, it would be great if you could take it out for some good runs when it is especially cold outside (approx -10C or colder). This will give us some worst-case data. Thanks!

 

[kup99]

kup99- no prob. I wasn't asking you to measure the EGR temp anyway. I was just stating that the resistor you are using (4.7kohm) corresponds to an EGR temp sensor temperature of about 280F.

As for your current setup, it would be great if you could take it out for some good runs when it is especially cold outside (approx -10C or colder). This will give us some worst-case data. Thanks!

O.K. as soon as temps get that cold I will let you know!!

 

[Ebag333]

The first thing I am confused about is intake air temp vs. ambient temp- the manual seems to use the two interchangeably as they do here: "When the EGR valve is open, the ECM compares EGR temperature to intake air temperature. If the temperature does not rise a specified amount over ambient temperature, the ECM assumes there is a problem in the system"

I don't think there's a way of distinguishing the ambient temp from intake air temp by the ECU.

The auto temp control LC's and LX's have a temp probe to measure outside temp, but non-auto temp control rigs don't, and it doesn't tie into the ECU anyway.

Intake temps will be pretty close to ambient. We're pulling air from the fender, not from the engine bay, so while air temps might be somewhat higher than ambient we're not talking about a 50* jump here.

So let me look at this again (thinking aloud and I'd be interested in your comments):

- When the EGR is supposed to be open, the ECU looks for AT LEAST a 95F increase in temperature over ambient/intake to verify the EGR is open, so assuming we're using ambient temp, then, yes, from your numbers it is looking for 109-235F to prevent a P0401. However, a temp greater than this is ok, so let's say worst-case we need T>235F to prevent a P0401 under cold or hot ambient temp.

No. The system test checks for 10* - 60* C (14* - 140* F) ambient in order to even test the EGR system at all. This is for both P0401 and P0402. If the intake temps are over 60* C (140* F) it won't throw a P0402, because it will say it's too hot to check it. If they are under 10* C (14* F) it won't test it either.

While the doc does say that the EGR system expects at least a 95* increase in temp to verify the EGR system is working, it doesn't say how much of an increase it allows for maximum, unfortunately. Obviously the system allows a huge range of variables without throwing a code, but that still means that the ideal range is somewhere in that 109* - 235* range.

Based on the values given in the FSM/EWD for the temp checks, it strongly suggest that a resistance of 64k to 97K Ohms means the temp is too low, and a resistance of 2k to 4k Ohms means it's too high. The FSM suggests that 11k to 16k Ohms is the ideal sweet spot, but perhaps one could read that as the "acceptable" range being from 4k to 64k Ohms, which would be roughly equivelent to that 109* - 235* range. The FSM doesn't specify where exactly the temp numbers it lists matches to the resistance, but my guess is they are only there to give you a rough idea anyway.

Ebag333- again, I've seen no evidence of people running the 1k resistors without problems in the OBD2 trucks we're trying to figure out here. Please do point me to some if I'm wrong- I'd love to make this simpler!

I'm going to try a 10K resistor (approx. 250F) and report back.

Exactly.

I think you're making this overly complex. Remember that I ran without any resistor for almost 1k miles (many of those on the freeway, where the EGR would have been active) without a code.

The system is not particularly picky.

Report back on your results.

 

[alaskacruiser]

I don't think there's a way of distinguishing the ambient temp from intake air temp by the ECU.

The auto temp control LC's and LX's have a temp probe to measure outside temp, but non-auto temp control rigs don't, and it doesn't tie into the ECU anyway.

Intake temps will be pretty close to ambient. We're pulling air from the fender, not from the engine bay, so while air temps might be somewhat higher than ambient we're not talking about a 50* jump here.

While I'm not sure if we have separate temp sensors for ambient temps that tie into the ECU, I can tell you that I've seen intake temps around 130F on my scangauge when ambient is in the 80s, and I don't think I'm alone in this from what I've read on the forums. The difference between ambient and intake temps I've seen range from 20-50F.

- When the EGR is supposed to be open, the ECU looks for AT LEAST a 95F increase in temperature over ambient/intake to verify the EGR is open, so assuming we're using ambient temp, then, yes, from your numbers it is looking for 109-235F to prevent a P0401. However, a temp greater than this is ok, so let's say worst-case we need T>235F to prevent a P0401 under cold or hot ambient temp.

No. The system test checks for 10* - 60* C (14* - 140* F) ambient in order to even test the EGR system at all. This is for both P0401 and P0402. If the intake temps are over 60* C (140* F) it won't throw a P0402, because it will say it's too hot to check it. If they are under 10* C (14* F) it won't test it either.

I think I wasn't clear the way I wrote it. The temp I was referring to with "T" (e.g., T>235F, T<157F) is the EGR temp sensor temperature (whether actual temperature or set by using a resistor). Let me know if you see something wrong in this:

(T = EGR temp sensor temperature)

1. To prevent a P0401 under all ambient temps under which the ECU tests, we need:
T>=(140F + 95F)
T>=235F
(or a resistance corresponding to this).

2. To prevent a P0402 under all ambient temps under which the ECU tests, we need:
T<=(14F + 95F + <TBD>)
(or a resistance corresponding to this).
(where TBD = To Be Determined).

Based on the values given in the FSM/EWD for the temp checks, it strongly suggest that a resistance of 64k to 97K Ohms means the temp is too low, and a resistance of 2k to 4k Ohms means it's too high. The FSM suggests that 11k to 16k Ohms is the ideal sweet spot, but perhaps one could read that as the "acceptable" range being from 4k to 64k Ohms, which would be roughly equivelent to that 109* - 235* range. The FSM doesn't specify where exactly the temp numbers it lists matches to the resistance, but my guess is they are only there to give you a rough idea anyway.

Without knowing the <TBD> value to prevent a P0402, this sounds like a good guess. Maybe I'll try something in the middle of that range- around 13-14k.

I think you're making this overly complex. Remember that I ran without any resistor for almost 1k miles (many of those on the freeway, where the EGR would have been active) without a code.
The system is not particularly picky.
Report back on your results.

Shorting the terminals of the temp sensor the way you did just set the EGR temp sensor value to some unknown maximum in the ECU (maybe 302F, maybe higher). The fact that the P0402 came on after 1k miles means that it eventually saw the temperature difference needed to trip the CEL. Perhaps it is because it saw just enough of a temperature difference as temperatures are cooling with winter approaching? I guess kup99's testing will help clear this up, as he is in colder temperatures. I haven't had time to set mine up yet, but will try this weekend.

 

[96r50]

FWIW, page DI-12 of my FSM lists the engine operating conditions. It also puts a disclaimer on them saying they are "representative values", so do not "decide whether a part is faulty or not solely according to the 'normal condition' here"

The entry under "EGR gas temp sensor value" is: "EGR not operating: Temp. between intake air temp. and engine coolant temp."

I dunno if this is useful or not, but I thought it might be relevant to this discussion.

 

[Ebag333]

While I'm not sure if we have separate temp sensors for ambient temps that tie into the ECU, I can tell you that I've seen intake temps around 130F on my scangauge when ambient is in the 80s, and I don't think I'm alone in this from what I've read on the forums. The difference between ambient and intake temps I've seen range from 20-50F.

Keep in mind that the temps tested are the starting air intake temps. That should be the ambient temperature, or fairly close to it.

In the case of where you've been runnning, shut it down, then start it right back up the starting air intake temps could very easily be above the 140* requirement meaning that the EGR system would not be tested.

I agree that it's not going to be exactly the same, but it's as close as Mr. T can get to it with the limited sensors availible.

Shorting the terminals of the temp sensor the way you did just set the EGR temp sensor value to some unknown maximum in the ECU (maybe 302F, maybe higher). The fact that the P0402 came on after 1k miles means that it eventually saw the temperature difference needed to trip the CEL. Perhaps it is because it saw just enough of a temperature difference as temperatures are cooling with winter approaching?

Hah! I almost posted something about that.

It was easily 90*-100* temps when I was running around, which the air intake temps could easily be even higher due to the fender/engine bay being hotter than ambient. 110* to 120* isn't unreasonable, and with the even warmer temps that the engine might record this could easily mean that the EGR system was never tested at all (above the 140* max), or only tested rarely.

It's certainly as good an explanation as any.

 

[alaskacruiser]

FWIW, page DI-12 of my FSM lists the engine operating conditions. It also puts a disclaimer on them saying they are "representative values", so do not "decide whether a part is faulty or not solely according to the 'normal condition' here"

The entry under "EGR gas temp sensor value" is: "EGR not operating: Temp. between intake air temp. and engine coolant temp."

I dunno if this is useful or not, but I thought it might be relevant to this discussion.

96r50- Thanks for the info. I don't have an FSM, but can you tell me the context of "EGR not operating"? Is this the same as saying "when the EGR is closed"?

If so, then I can revise #2 as follows:

(T = EGR temp sensor temperature)

1. To prevent a P0401 under all ambient temps under which the ECU tests, we need:
T>=(140F + 95F)
T>=235F
(or a resistance corresponding to this).

2. To prevent a P0402 under all ambient temps under which the ECU tests, we need:
(14F<=T<=(COOLANT TEMP)
(14F<=T<=(184-230F) (with some margin)
(or a resistance corresponding to this).

 

[alaskacruiser]

Keep in mind that the temps tested are the starting air intake temps. That should be the ambient temperature, or fairly close to it.

Ebag333- from the info you posted from the FSM, it states:

P0401: Insufficient Flow
When the EGR valve is open, the ECM compares EGR temperature to
intake air temperature. If the temperature does not rise a specified
amount over ambient temperature, the ECM assumes there is a problem
in the system, and this information is stored in the ECM. If the problem
occurs on the second trip, DTC P0401 will set and the MIL will turn on.

P0402: Excessive Flow
When the EGR is off, the ECM measures EGR temperature. If the EGR is
open, the EGR temperature will be higher than expected. If the problem
occurs on the second trip, DTC P0402 will set and the MIL will turn on.

Does it state anywhere in the FSM exactly when and how often the EGR test is performed? Is it only performed once per starting cycle the first time ambient temps are in the proper range (as you seem to state)? Or does it continuously monitor the EGR during driving to verify the EGR is opening and closing properly?

 

[Ebag333]

Does it state anywhere in the FSM exactly when and how often the EGR test is performed? Is it only performed once per starting cycle the first time ambient temps are in the proper range (as you seem to state)? Or does it continuously monitor the EGR during driving to verify the EGR is opening and closing properly?

Page 3 in the PDF that I posted answers all of those questions.

 

[96r50]

Honestly, I'm not really sure what to make of it. Here is the section it came from (last page).

 

[alaskacruiser]

Page 3 in the PDF that I posted answers all of those questions.

Ebag333- I just read over pg. 3, and here's what I see for "enable criteria" for testing:

1. Run time > 160sec

2. Coolant temp at engine start = (140F-221F) (looks like one of the conditions is a "Warm start")

3. Air temp at engine start = (14-140F)

4. Batt voltage >= 11.0V

5. Throttle Position = (9-14.7) (only applies to P0402)

6. Closed Loop Mode

7. Vehicle speed = (increasing for 3sec.) (only applies to P0401)

8. Drive cycle; During purge operation- (can someone tell me what this means?)


Maybe I'm not seeing something, but I still come away with the same question: FSM says "run time > 160sec". Does this mean it only tests once after 160sec, or that it can test any number of times after 160sec depending on the other conditions?

 

[Ebag333]

Maybe I'm not seeing something, but I still come away with the same question: FSM says "run time > 160sec". Does this mean it only tests once after 160sec, or that it can test any number of times after 160sec depending on the other conditions?

It can test any number of times after 160 seconds as long as all other criteria are met.

8. Drive cycle; During purge operation- (can someone tell me what this means?)

I believe this refers to the EVAP Canister.

Not Toyota, but should give you an idea on how it works.
http://www.asashop.org/autoinc/feb2006/techtips.htm

 

[tblume]

HAHA OBD II sucka's


I keed, I keed.....

 

[alaskacruiser]

It can test any number of times after 160 seconds as long as all other criteria are met.

In which case, this statement is not accurate:

Keep in mind that the temps tested are the starting air intake temps.

I believe this refers to the EVAP Canister.
Not Toyota, but should give you an idea on how it works.
How Nissan Evaporative Systems Work

Reading...thanks!

 

[Ebag333]

In which case, this statement is not accurate:

They are two different checks. They are both true.

When you start the engine it checks the air temp and the coolant temp. If they are in range, then it will proceed with the rest of the checks. If they are not in range, then no further checking will be done.

If that statement is not true, then it's Mr. T who's wrong, not me!

1. Run time > 160sec

2. Coolant temp at engine start = (140F-221F) (looks like one of the conditions is a "Warm start")

3. Air temp at engine start = (14-140F)

 

[Land Speeder]

FWIW... I went from 8mpg to 12 mpg... this was after a HG replacement and then EGR system bypass. I credit the bypass since every part of my EGR system was clogged...

 

[kup99]

temps are starting to get colder here!! I'm well over 200 miles with no CEL. I should be able to do a bunch of cycles in a good temp range this weekend!!

I'll keep you posted!!

 

[kup99]

O.k it's been between -10* and -15* in the mornings this week. I've been driving to work, and to the rink (which is work) a few mornings, and no CEL. Im well over 250 Miles since I did the 4.7K ohm resistor trick and have not had an issue! Next weekend my plan is to do about a 750km round trip with both highway and city driving!

I'll keep you posted!!

 

[Ebag333]

Thanks for the updates.

 

[alaskacruiser]

Update: Just back from road trip. 700 mi. completed using 10k resistor, blocked vac lines, ambient temp range 30F - 70F. No CEL as of yet. Will keep you guys updated...