This is one of the best videos about the operation of a Toyota/Geo Prizm and others, use to control EGR. I work at dealerships and a few other shop, but cut my teeth on imports. Manufactures have different names like “ EGR back Pressure Transducer “ but EGR is mid-understood. If it has this small hole on the diaphragm, cold idle will be higher than normal. Yes, the exhaust has back pressure and the tuner crowd can mess this up. Others stick “BB’s” in the vacuum lines, get the code, but if you have EGR at idle, it will run rough, bad. EGR allows inert gas to enter the combustion chamber, this allows the temperature to drop and reduces the production of NOX. A low level smog, like raw gasoline. In California, they use a temperature sensor, a 1 wire thermistor that changes resistance when heated by EGR. The other states simply close the (VSV) vacuum switching valve during normal EGR Op’s. The ECM watches for changes in air-fuel ratio over a period of time, driving down the highway. EGR is inert. Meaning it does not react to air & fuel & spark, so the normal A/F ratio goes lean, but comes back once testing is done. There is more to known about system on a vehicle than most of the human body. This is September 12, 2020. I noticed 4 thumbs down. WHY. You like to see fingers? It did not diagnose the entire EGR system? Say what? Hit the like button. He cut this aftermarket part in two at the crimp band, then showed you where vacuum goes and what goes wrong. The OEM EGR back-pressure transducer uses a RED high temp silicone in this area. Hello, it’s exhaust pushing up on this diaphragm. As a Retired ASE Master Tech from the 70’s, I hit the like button. This car has been in our family for 20+ years and had the EGR low flow code (I have a Scan-Tool) but took my hand vacuum pump under the hood to test and confirm. Knowing how stuff works is valuable. If you don’t fix it, some outfit who pays their techs (Who Own Their Tool Boxes, $10k SnapOn X 4 for me) but they give them 20% of the parts they sell. Ask! If they are not paid “Flat Rate” run fast. This video is information to learn as this device is used on Acura’s, Subaru’s and others. Hey, let’s talk “Boost Control Deceleration Device” and what it’s for and how it works? Oh, it’s EFI, the injectors shut off during deceleration, so your exhaust does not fill up with gas fumes and blow-up when the system turns back on before your stop at the Red light! Hit the like button and subscribe, you’re never to old to learn. Thanks! Great video ;) Retired ASE Master Tech since the building said Datsun on it.
Have any advice on checking the vacuum switching valve when It is out of the car (short of taking it apart)? Also, how do we repair/replace the back seat 'over-the-shoulder' seat belts?
@@jimcarey160 For a vacuum switch valve, it can be 5Vdc or 12Vdc. Test the signals first and check for ground. I don’t know the Toyota Corolla/ Geo Prizm by heart, but “VSV’s” rarely fail. The diaphragm in the EGR system is opened on purpose by the clock in the PCM on purpose to test it. It dumps exhaust into the combustion chamber and makes it run lean. The PCM/ECM performs this test on purpose to make sure it is working. The “VSV” with hoses can blow thru or be closed. Start a “Truth Table” to write results. Apply vacuum to the EGR at idle and if good, the engine will die. The seat belts retractors are tricky. They say “Do Not Repair” on them. I have tightened the coil spring to make it retract better but no luck. Find a good one in the local bone yard and snatch it. Some can be fixed, others, not so much. All use a simple “Pendulum” to move and lock up. Pull slowly and hit the “B” pillar with your hand or dead-blow hammer. It should lock. If the problem is with retraction, I have had little luck fixing those and I have tried hard. I am frugal and will try to fix before buying. Door lock hardware in rear door rust and stick & won’t open. It is a day long job to R&R one, lube it with old school oil can & motor oil. Not WD-40! It dries and is gone in 15 minutes. Best of luck!
Thank you, thank you, thank you. I finally found out the modulator is bad because you explained how it works. I’ve looked everywhere & no one else showed it. Plus you get to the point right away & explain it.
Finally! A vid that actually explains clearly how these work! Dealing with a P0401 code and occasionally a P0446 code on my 99 Camry, 4cyl, CAL emissions. Thanks for the details. ;-)
today I got around to doing some work on the car. first thing on the list: pop that lid off the modulator. without removing it from the clip... I used a bent nose needle nose pliers, using the bend for leverage, the tip under the edges, and that cap came off rather easily, much more easily than I imagine. Using a piece of 12 gauge wire, I lifted out the filter(when re-installing make sure the course side is up, naturally, the smooth side down) Man! was it absolutely filthy!!! used the compressor to blow it as clean as I could. Used no liquid of any kind. I noticed a black dot underneath the filter, I think this indicates carbon or soot from one of the hoses, don't know which. It may indicate a through cleaning of the throttle body and its components maybe necessary. Any way, thank you for this presentation, it was a tremendous help. Thumbs 170!
Close but not accurate. The two ports on the throttle body are one pre throttle plate and one post throttle plate. You will notice the one has vacuum and the other not. When there isn't enough backpressure to command the diaphragm on, the vacuum line after the throttle plate labeled P (essentially manifold vacuum as its after the the throttle plate) pulls vacuum through the modulator tee and into the bottom side of the regulator and then back through the bleed hole to the top side or the regulator and back out the return line back to the port R that is before the throttle plate (or air filter side of the throttle plate, not manifold vacuum). When egr is commanded by the egr backpressure and the diaphragm closes off both ports on the bottom of the regulator. you can see how both ports would be covered by the seal of the diaphragm at time 4:19. The witness mark is there that shows both are blocked. This then bocks the return path to create a positive seal for the vacuum to continue on to the solenoid switch, then on to the egr valve. The R line never pulls vacuum. It just pulls filtered air after the air filter but before the throttle plate to complete the circuit when egr backpressure is insufficient to lift the valve. I not trying to argue but you can study the system in all data and it clear it works this way. Hope this helps some of you.
what else you got,? Evap system maybe? I'd pay to see you explain that. It's not difficult, but seeing how the pieces interrelate, and the order of operations is key to understanding how things work.. BAck in the day this is how i learned the inner workings of appliances. thanks
Wow, this is a great video for a novice (like me). We have a '95 Corolla (1.6L/auto-trans) that recently failed it's smog/emissions test for high Nitrous oxide test at 15 mph. Interestingly enough, it passed the NOx at 25mph?? No check engine light & car runs great! Took the car to a local shop & kid there says he couldn't get a vacuum on the EGR?? My son helped me remove the EGR & EGR pipe/tube (we couldn't get the EGR off by itself). Cleaned off a little carbon build-up on the needle valve. Was able to get vacuum but had to block 2nd port while drawing vacuum off the first port (wonder if the mechanic realized he needed to do this when he did vacuum test??) Pointed flashlight up one end of EGR pipe and couldn't see any light coming through to the other end (Blocked??). Cleaned out EGR pipe/tube with metal hanger. Wondering if a blocked EGR pipe/tube could have been problem all along. I want to make sure everything works before I take it back to smog shop again ($$$) so I am going to check the Vacuum switching valve and the modulator valve. This video helps TREMENDOUSLY. is there anyway to test the modulator that is 'out-of-the-car? Have any videos about checking the vacuum Switching Valves? Anyone else have any thoughts or advice?
great video well explained thank you. I should do one on TVSV : I ve repaired/redone 3 operating ones out of 5 from the start . either the piston's seat is cracked thus connecting ports incorrectly or the bimetal has decreased in stroke/strenght ; piston's stroke shortened. salvageable only if the seat is cracked just turned 2 others from aluminum. great video again tomorrow I have 2 modulators (canada m/t)with 3 ports only , ( a lot of 2 ports too a/t usa/federal) all TOYOTA from 83-87 been driving tercel4wd for last 25 years . now i ve seen the internals i might not open them hopefuly ... thanks again
terrific explanation! I suppose that I can pop that top cover part off while it is still in its holding clip.(thus avoid removing hoses) Then remove the fiber filter and blow clean it with my compressor.
Thanks for the great video! Just done a smoke test on my 2001 Camry. A lot of smoke came out from under the EGR modulator cap. So it must be a broken diaphragm? Problems have been rough idle and erratic rpm after cold start, high LTFT, while no CEL, no code.
Awesome explanation of how these thing work. Btw, I had a hard time looking for a filter for this unit on my '93 2nd gen 4Runner. Can I just replace it with a small cotton ball as a filter? TY in advance
Sure thanks; and thank you for taking your time to teach your knowledge and making such an informative video. watching your video I feel I am that much smarter now. I have a question now. I was tracing code P0401 on my 96 Toyota Camry 2.2L engine. I took the EGR modulator out, I happen to find a good few drops of water coming out of the "R" intake hose. I am wondering if this moisture is normal to be in it? I live in Southern California and we don't have that much moisture in the air.
So... when I need power [say half throttle] the modulator control is there to cause egr to dilute intake charge and give me that half second lag I don't want as sensors/computer catches up to engine conditions, and available horsepower is reduced. Great. But the video is perfect - thank you! I get intemittant P0401 codes, and [after cleaning egr and throttle body port] either this modulator or the solenoid connecting Q port to the egr is going bad
Good explanation and without a lot of extraneous verbalization. I now understand how this thing works. I don't quite understand how this part breaking would cause a code P0402 which is excessive exhaust gas flow as opposed to code P0401 (insufficient gas flow). Does any one know?
1993 celica with 2.2 runs really bad under 3,000ish rpm’s above that cleans up and runs great! New timing belt and timing is set at factory specs. Any ideas?
@@personalfunfest while we're at it, (unless I missed it), my port P is closed when cold, so it holds vacuum. Bench testing the modulator by pressurizing on the EGR port shouldn't that relieve the vacuum in port P that I applied? And if not that means the modulator is bad, right? You explained that at the 5 minute part but there is no video on RU-vid bench testing this procedure. Hint hint!
@@personalfunfest with my current "used" Modulator when I try to pull vacuum from Q it doesn't hold. Then when I apply air pressure from EGR port on bottom then I can draw/hold vacuum from port Q while plugging port P. If I release port P the vacuum decreases slowly. Does that sound like its functioning correctly? Thanks again! :)
It's normal position is 'Open' or 'Closed'? Does the spring push Up to plug or Down to open? A diagram of the section of the valve would have helped a lot.
Damn i have code 71 for my 1995 4runner i chnaged the egr it went away but the light came back n how can u know if your modulator long longer works properly?? 🙏 thanks great video new sub to your channel!
Im having am MTM 3RZ with failed modulator,,, i only found the one from ATM 3RZ and installed it. Shall it cause any inefficiency? Origanal pn for MTM 25870-75040. What i put is from an ATM 25870-75030
I have a smoke tester and I have smoke coming from the egr vacuum modulator, good chance I have that same hole? At idle I have a idle surge, sounds like a vacuum leak.
There should be no smoke coming from the egr vacuum modulator? Truck is off and and smoke testing it after I had the truck warmed up, 94 toy pickup, 2.4l
Is the EGR Modulator shown in the video an OEM modulator? My 1998 Toyota Rav4 has similar numbers embossed on the lower edge, as shown in the first 16 or so seconds of the video. I want to know if my modulator is OEM.
@@personalfunfest Thank you for your prompt response! I am driving in the mountains lately for camping trips. Once in awhile while going downhill and decelerating (to control speed), my Rav4 throws a P0401. It never throws this code when driving around town, for weeks on end. I am enjoying troubleshooting. I still need to run some tests on the modulator (for my education mostly), but the fact that it is aftermarket does say a lot to me. Your video rocks :)
personalfunfest I’m not sure I understand - If p and q are in a T shape tubing with the bottom vent, and they are all attached to vacuum hoses, where does the particulates come from? My EGR modulator doesn’t have the R nozzle - it’s just P and Q. So where would the ‘outside’ particulates come from??
personalfunfest Sorry to be a pain....so the the tube going from p to q, with the opening coming up from the bottom nozzle, is not and enclosed T? There are openings somewhere else in the modulator, other than those 3 nozzles? There are vents somewhere? Edit: For example, if I close off the bottom nozzle and P (assuming only P and Q on the top) can I blow through Q??
![How Toyota EGR Modulator works [Everything you need to know!]](/img/logo.svg){kind=logo}
