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Egr Inspection & Cleaning (1993-2002)

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Exhaust Gas Recirculation Inspection & Cleaning for 1993-1997 Mazda 626
(1998-2002 models please scroll down to 2nd post)

Current Models Covered: 1993-1997 All transmission and engine types.
(will be adding 5th gen info soon)

This tutorial covers all models of 1993-2002 Mazda 626's but please be aware that your EGR might look different from what is shown here. The 626 in those years have at least 3 different EGR's and all look and perform slightly different from one another. For the purpose of this article we will be using a 1995 Mazda 626 2.0L EGR because that's the only one I have. :)

You should clean the EGR about once every decade or when you believe the EGR is malfunctioning. Depending on the amount of carbon buildup you might need to clean it more or less than others. Your situation will be different from the next person over the life of the car. No two cars will have the exact same amount of buildup due to a myriad of factors. If you are reading this then it's likely you believe it's time to inspect your EGR.

If your car is currently non-functional or it has a no-start condition you will not be able to fully test the EGR. However, you can still get a very good sense if it is mechanically and electronically functional by skipping to step 2.

The EGR operates ONLY when the following conditions are met:
Throttle Position Sensor, Mass Air Flow Sensor, Coolant Temperature Sensor, Intake Air Temperature Sensor are functioning normally
Not cranking
After warmup
Engine between 1000 and 5500 RPM.
Engine temperature not below 78F (we're not talking about ambient temperature here, it's actual engine temperature, so basically winter conditions).
Not under heavy load

Step 1 - Vacuum Test (Engine Running) (requires vacuum pump)
The first thing we want to do is test the EGR position sensor for resistance and continuity while the car is running. Start the engine and let idle. Remove vacuum line from vacuum port on top of the EGR.

1993-1997 All Engine & Transmission Variants
Connect vacuum pump and apply 5.4-7.7 kPa vacuum.
Verify the engine runs rough or stalls at more than 7.7 kPa vacuum.
If it stalls prior to 7.7 kPa replace the EGR.

If you don't have a vacuum pump a very quick (but not technically proficient) test is to fully depress the diaphragm and hold your finger on the vacuum port as you release the diaphragm. Leave it there for a minute and see if the diaphragm or piston/shaft moves. It shouldn't move, it should hold vacuum precisely how you left it. Doing this test will leave a little circular mark on your finger.


Step 2 - ECU Voltage Test (Engine On not Running) (requires vacuum pump & multimeter)
Backprobe the EGR harness for voltage with no vacuum applied.

1993-1997 2.0L (Manual & Automatic Transmissions)
Pin C = 0.8v
Pin B = 4.5-5.5v
Pin A = 0v

Connect vacuum and apply 20kPa and measure voltage on Pin C.
Pin C should now be at approximately 4.9v.

1993-1997 2.5L (Manual & Automatic Transmissions)
NOTE: The 1995 manual has a discrepancy which differs from the 1994 manual for the V6 pins that someone needs to figure out. The 1995 pin labeling is B,A,C. The pins lead to the exact same locations on the ECU. All readings are still the same as listed above just in a different order. Whether this is a mistake in the manual for the V6 or a change in how the sensor was produced needs to be figured out by V6 owners. I don't have a V6 and cannot help more than making you aware of the discrepancy.

Pin C = 4.5-5.5v
Pin B = 0v
Pin A = 0.8v

Connect vacuum and apply 20kPa and measure voltage on Pin A.
Pin A should now be at approximately 4.0v.


Step 3 - EGR Position Sensor Resistance Test (Engine Off) (requires vacuum pump & multimeter)
Disconnect EGR vacuum hose and reattach vacuum pump (if not already attached). Measure resistance (ohms) between the following terminals.

1993-1997 2.0L (Manual & Automatic Transmissions)
Pins A & B = 2.7k Ohms
Pins A & C = 0.5k Ohms
Pins B & C = 2.4k Ohms

1993-1997 2.5L (Manual & Automatic Transmissions)
Pins A & B = 0.7 to 5.0k Ohms
Pins A & C = 0.7 to 5.0k Ohms
Pins B & C = 5.0k Ohms

Now apply 20kPa and measure resistance between the following terminals.

1993-1997 2.0L (Manual & Automatic Transmissions)
Pins A & B = 2.7k Ohms
Pins A & C = 2.7k Ohms
Pins B & C = 0.1k Ohms

1993-1997 2.5L (Manual & Automatic Transmissions)
No information available.



Step 4 - Cleaning
If you're done all the testing and you believe your EGR is slightly out of spec and might be stuck due to carbon build up you can easily clean it and re-test it both on and off the car. This could potentially save you over $100 for a new EGR. For cleaning you must remove the EGR from the car. That can be a tricky proposition for some versions where it's located below the throttle body. If you need help locating and removing your EGR please do a forum search as those topics have been covered many times already. Step 4 begins after you've removed the EGR.





Supplies: Multimeter, pick tool (very important), carburetor cleaner, PB Blaster or WD40 (not pictured), automotive grease (not pictured), phillips screwdriver, rags.
Time Estimation: 1 hour

Now that you've got the EGR out and are ready to proceed with cleaning go ahead and measure for resistance again. Compare it to the values received when it was in place on the car. There shouldn't be any difference in the values. If there is it's possible you have a bad sensor. Shake it a couple times and listen for loose debris in the EGR or the sensor itself. You shouldn't hear any.

Let's inspect the diaphragm for any obvious cracks or tears. You can push down on the diaphragm with fingers from each hand (if you only have 1 hand or missing fingers a slide lock vice might help). The diaphragm and spring should move up and down. There is a possibility that it is stuck so don't force it too hard. We'll get to that part next. This image shows the diaphragm fully open. It takes a good amount of force with your fingers to open it all the way.


Before we begin cleaning it might be a good idea to explain how the EGR diaphragm works so that you can avoid contaminating it The diaphgram itself has a large spring attached and depending on the vacuum pressure depends on how much the piston goes up or down which in turn allows EGR gasses to flow into the intake manifold.


Let's remove the EGR position sensor. Here you can see the sensor is a very simple mechanical plunger. The travel in the plunger will change the electrical resistance (ohms) you get out of it. You can remove the sensor and do a resistance test exactly like in Step 3 with 0 vacuum.


Here is what it looks like inside the sensor housing. Notice there is a contact point for the tip of the plunger. Make sure that contact point and the plunger aren't broken or worn down.


We start off with a dry cleaning. Do not use carb cleaner yet. Use your pick tool and scrape out as much carbon as you can. It's likely to be formed in there the same way super thick ice forms to things in the winter. You might need to crack large bits of it out there. It cracks similar to ice too. It's MUCH more efficient to clean dry carbon than wet carbon. It's the same concept as trying to sweep sand vs mud. Get as much done with scraping and using a pick tool as you can. I recommend getting an angled pick tool as shown in the supplies picture above. That thing was the perfect tool for the job. Other good tools to have would be pipe cleaners, tiny bottle brushes, and a small wand style steam cleaner.

Now that we've cleaned out as much carbon out as possible we go with the carb cleaner. I used some legos to prop up the diaphragm. It takes a good amount of force to keep it open and it wears on your fingers after a couple minutes so use whatever you can to keep it propped open during cleaning. Your fingers will thank you. Spray the heck out of it but don't tip it upside down. You don't want to chance getting carb cleaner on the delicate rubber diaphragm. It wouldn't be good for longevity.


After you cleaned it to the point where the diaphragm easily opens and closes you will want to lube the piston up a bit. It would be silly to do this while cleaning as the carb cleaner will probably just eat it. Depress the diaphragm one last time until you can see the diaphragm shaft then use a qtip and some silicon based grease. Do NOT EVER use PB Blaster, WD40, or any petroleum based lubrication especially not packing grease, if that stuff contacts the rubber it will very slowly eat away at the rubber over 6 months to a year and the rubber will look like acid was poured on it.  Petroluem based rubber vs petroluem based grease = bad.  When lubricating anything rubber ONLY USE SILICON BASED GREASE! Open and close it a lot to help the lubrication get in there and your ready for reassembly.


If you think your intake manifold has a carbon clog or you just want to clean it here is how.


A pick tool like this can be an invaluable asset to your toolbox. You can pick one up at any auto parts store for a couple dollars.


You will need a rather large allen key to get at the EGR cleanout. It's also locked in with thread sealant and heavy torque. You'll need to brace yourself to break it loose.


Keep in mind if you remove the intake manifold or EGR from the car that the gaskets will more than likely need to be replaced.

Here's is another great video on EGR cleaning from BriansMobile1 for the Protege.  It's identical for the Protege, 626, MX6, and Probe 2.0L EGR systems.





Edited by djdevon3
updated lubrication step to warn about petroleum based grease on rubber
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  • 2 weeks later...

Exhaust Gas Recirculation Inspection for 1998-2002 Mazda 626


Step 1 - EGR Position Sensor Resistance Test (off vehicle inspection)
Disconnect EGR vacuum hose and reattach vacuum pump (if not already attached). Measure resistance (ohms) between the following terminals.

1998-2002 2.0L & 2.5L (Manual & Automatic Transmissions)
You should get exactly 22 ohms of resistance between the following pins @ 73*F.  The measurement values are for 73*F.  You will get a different result at 80*F and 90*F depending on outside weather.  You must account for temperature difference causing a difference in the wiring resistance.
Pins C & E
Pins C & A
Pins D & B
Pins D & F

That's all there is to the inspection. If the resistance is out of spec you have to replace the entire EGR valve. For cleaning please refer to the 1993-1997 procedure as it is the same. Prior to any cleaning either remove the sensor from the housing or be careful enough not to tilt it upside down while using liquid cleaners.

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  • 1 year later...

Thanks Devon, I think with this information I can manage to figure out what resistors is needed to remove the EGR error codes if it is removed from the car :D


1993-1997 2.5L (Manual & Automatic Transmissions)
NOTE: The 1995 manual has a discrepancy which differs from the 1994 manual for the V6 pins that someone needs to figure out. The 1995 pin labeling is B,A,C. The pins lead to the exact same locations on the ECU. All readings are still the same as listed above just in a different order. Whether this is a mistake in the manual for the V6 or a change in how the sensor was produced needs to be figured out by V6 owners. I don't have a V6 and cannot help more than making you aware of the discrepancy.

I got a 95 and will try to figure this out for you :)

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I've learned quite a bit about automotive circuit design since then. Generally anything that is steady 4.0-5.0 volts (pin C for example) is a "reference voltage" that the ECU uses for diagnostic purposes. It tells the ECU if it can communicate with the EGR sensor. In computer terms it would be a ping. It pings that sensor every couple milliseconds. If something is ever off with an EGR sensor on a 1993-2002 Mazda 626 the ECU will set a CEL within milliseconds of it happening. Seriously it will. That only applies to the plunger sensor itself though not the diaphragm or an EGR clog, etc.. On the 2.5L Pin B at 0v is likely the ground wire. Pin A which fluctuates between 0.5v and 4v would be reporting the position of the EGR sensor to the ECU using variable voltage. It's probably some kind of potentiometer or pressure sensitive transducer I still don't know exactly how the position sensor regulates it's output voltage.

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  • 2 months later...

1993-1997 2.5L (Manual & Automatic Transmissions)
Pins A & B = 4,76k Ohms
Pins A & C = 5,96k Ohms
Pins B & C = 2,91k Ohms


1993-1997 2.5L (Manual & Automatic Transmissions)

Pins A & B = 4,74k Ohms
Pins A & C = 1,04k Ohms
Pins B & C = 5,80k Ohms

Short on time when measuring so those values may be wrong.

I used the vaccum port on the engine but I am asuming it is close to 20kPa.

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I double checked my measurements, they seems to be OK. I figured out how to use resistors but it will require som diods aswell in order to be able to remove the EGR without any error codes, now what I am doing is using the EGR, sawed the bottom part away so the sensor and vacuum still work and take less space, I will place it down there and hook the vacuum up as normal.

Dj, I noticed my 95 got an EGR that looks like the one you have pictured in the post, but the ones I got from 93-94 got 3 wires comming out and plugs into the engine harness, so is that the EGR for the US version of the 93-94 model?

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Figured it out, the 93 had a different version and on ebay where they sell some they usualy contains the adapter harness needed. I have yet to figure out which pins is different fron the 93 to 95...

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Got the 93 to work on my 95, not sure on what pins is what, but I atleast know the coloring codes, might help you?

On the 93 it is Green to 95 Green. 93 Black to 95 White with red mark and 93 Red to 95 Black.

I got a plugs from the 93 EGR vent and the one from the 95 wiring harness, I was a bit unsure of what pin is what since the 93 EGR had wires comming out of it into a female plug, and the 95 has a female plug on the wiring harness.

I'll take some pics next time and so we might be able to figure it out :)

So great you got so much info on these cars, and on the v6 aswell, even tough you don't own any :P

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  • 6 months later...

I pulled a couple from junkyard 626's.  1 of the sensors has readings that are in spec and 2 are out of spec.  The one I have is barely in spec and is working for the time being.  I haven't thrown an EGR code in a while.  As long as you aren't throwing an EGR code your system is working as expected.  The EGR sensor is monitored and if it's not functioning as intended will set a code.  That includes codes being set by low flow (clog, restriction, diaphragm) or a faulty sensor.  It's up to you to determine if it's a flow issue or sensor issue on the 93-97.


The 98-02 owners have it much easier with OBD-II as the ECU will tell you if it's a flow issue or sensor issue.


If I absolutely needed to get a new EGR sensor I would probably buy it from RockAuto.  If RockAuto doesn't have any then you can probably source it from a local auto parts store.  If you're desperate then expect to pay an arm and a leg for a new EGR sensor from a dealership.

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Thanks DJ. Definitely dealer is out of reach. I found this at AutoZone website with 20% discount and free shipping for $136.95. Hope it will work.





I tested the EGR solenoids and they are good, they are allowing the air flow according to the manual. There is no vacuum leak now, earlier there was. Even after cleaning the EGR valve it is still having DTC P1407 so I'm going to replace the EGR valve. I tried with junkyard one but that did not work either, resistance values are even lower than mine so I guess I have to replace it.


Wish me best of luck.

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  • 1 year later...

How common is it for the 98-02 2L egrs to have clogs or failures which cause them to be stuck open when they're supposed to be closed?  I'm suspecting that my somewhat rough low idle and engine wobbling / shaking on medium to heavy acceleration or WOT might be caused by a stuck open egr.

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A MIL (malfunction indicator lamp) is a generic term for a CEL (check engine light), O/D off blinking, ABS blinking, traction control blinking.  Any of those lights that turn on in a way to indicate a fault is considered a MIL.  Usually when you hear the term MIL it's usually as a CEL because it's the most common MIL.

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If you are following the procedure outlined on page 01-16-7 of the 1998 work shop manual then yes that's a fair ohm reading taking into account ambient temperature difference from the 78F they always use as a base ambient temp.  I'd say you are perfectly within spec.  To confirm this you can wait for a day later this fall that is 78F and retest.  I bet you'll find that your spec is very close to the expected value of 22 Ohms.  You cannot remove the part and take it inside and set your A/C to 78F because the test requires the sensor to be plugged in on the car.  It tests the resistance of the wiring directly between the ECU and the sensor.  Since it's a resistance test that means resistance is very important to the functionality of that sensor.  The ECU likely interprets data from the sensor in resistance values and not just voltage. 


I'm not a fan of when engineers setup sensors to operate in that fashion but we're stuck with it, nothing we can do about it.  You have to test resistance on the car when it's 78F.  They do not print that part in the manual it's expected because every other resistance test they show from 1993-2002 always states that they're testing environment is 78F (the inside temperature of their engineering department).  Since resistance will change with ambient temperature you can compensate a little for that.  On a hotter day you add a little bit of resistance, and on a colder day you subtract some.  Unless you can figure out a calculation to know exactly the resistance difference (diameter of wire, material of wire, exact length, temperature difference) then you're basically guessing at the resistance differences between their spec and your ambient temp.  Hope that makes sense.


That's why it's easier to just wait for a 78F day.  I know that's unrealistic during most of the year.  For the rest of the year when compensating for ambient temperature you just have to make an educated guess.  Since you're only off by 1.5 Ohms that's why I'm inclined to believe you are perfectly within spec.  Usually they will include a chart and different expected resistances at different temperatures.  Sucks they didn't make a diagram like that in this instance.

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