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Discussion Starter · #1 ·
My 2000 SL600 continues to throw a P1490 code. I've re-worked the hoses into and out of the Evap valve behind the left headlight, and have a solid vacuum connection at the valve. Forty eight miles later, P1490. I removed the evap valve, cleaned it and tested it on the bench, and it works fine. Forty eight miles later, another P1490. So I replaced the valve with a new one. What happened after 48 miles? Yup, another P1490.

Has anyone else had other problems that have resulted in a P1490 code? Clearly the valve is not the problem.

Any suggestions as to how I can further diagnose this issue?

I need to get at least 50 miles without a CEL to pass my local state inspection, and this is driving me cRaZy!
 

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I have an SL 600, MY97 with the V-12 motor. My introduction to the car a few
months ago showed a string of errors associated with the Purge Valve system.
I know that a production change was made for MY98 and on with regards to
the placement of the charcoal cannister and am not well versed in the use of
the WIS/ASRA database. I do want to present the idea to you that most likely
you have a vacuum line leak. You just haven't found it yet. Attached find what
I used for my car, yours may be a bit different, however, the concept will be
similar.

Take a look at the 120 engine vacuum line diagram. I had faulty or broken lines
on my left purge valve as well as the pressure sensor. This is important as the
computer commands the purge valves to open so the fuel vapors can enter the
throttle bodies. It know the system is works my monitoring the pressure
pulses that are sensed by the B4/4 sensor. I anticipate your issues will be in
the engine compartment as that is where the lines will rot the quickest due to
heat.

My problem trying to help you is I am unable to get the equivalent diagram
for your MY2000. Do not give up yet, it is most likely you have not located
the faulty line. If you can get the equivalent block diagram for your MY2000,
you might be able to locate the line quickly. Sorry, this is the best I can do
for now. Best of luck.

Paul
 

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Discussion Starter · #3 ·
I have an SL 600, MY97 with the V-12 motor. My introduction to the car a few
months ago showed a string of errors associated with the Purge Valve system.
I know that a production change was made for MY98 and on with regards to
the placement of the charcoal cannister and am not well versed in the use of
the WIS/ASRA database. I do want to present the idea to you that most likely
you have a vacuum line leak. You just haven't found it yet. Attached find what
I used for my car, yours may be a bit different, however, the concept will be
similar.

Take a look at the 120 engine vacuum line diagram. I had faulty or broken lines
on my left purge valve as well as the pressure sensor. This is important as the
computer commands the purge valves to open so the fuel vapors can enter the
throttle bodies. It know the system is works my monitoring the pressure
pulses that are sensed by the B4/4 sensor. I anticipate your issues will be in
the engine compartment as that is where the lines will rot the quickest due to
heat.

My problem trying to help you is I am unable to get the equivalent diagram
for your MY2000. Do not give up yet, it is most likely you have not located
the faulty line. If you can get the equivalent block diagram for your MY2000,
you might be able to locate the line quickly. Sorry, this is the best I can do
for now. Best of luck.

Paul
That's incredibly helpful, thanks! Where is your B4/4 sensor located?

Mine appears to be under the HVAC airbox behind the firewall, an area inaccessible without removing the HVAC airbox, which ain't gonna happen. The Y between the two evap valves also appears to be in the same area.

I did inspect the lines to the second evap valve, then found the lines going to the evap canister in the trunk. Armed with your diagram, I disconnected the lines at the canister and vacuum tested them. The lines going forward from the canister to the engine all hold a vacuum (10 on my gauge, for at least 10 seconds.) So I don't suspect any leaks from the canister forward. The canister itself will also hold a vacuum just fine (with no lines attached and holes plugged.) With the vent lines attached, it obviously doesn't hold a vacuum, and you can hear the air hissing under vacuum (I suspect an orifice of some sort inside the canister to allow vacuum to build so the B4/4 sensor can detect it.)

I reset the CEL and I'll drive s'more. Thanks again for the diagram.
 

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1997 Mercedes SL 600 w/automatic tx
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Attached find another diagram. My car is like the one on the left of the
page. It sits in the engine compartment on the driver's side. The vacuum
line from the sensor runs outboard to a covered channel area. The hose
length of roughly 8 inches was exposed in the engine compartment and
rotten. I cut it behind the area where it was covered and spliced a 3 mm
piece of hose and everything worked well after that.

Given that you are not having any vacuum leaks, you might want to take
a look at the purge valve operation. After start up, with both purge valves
exposed, see if you can determine whether or not the valves are being
pulsed at a say three cycle per second rate. You might be able to feel the
pulsation with your finger and if it is easier, use a long screwdriver as a
stethoscope to see if they are pulsing. The valves may not be activating.

It does seem odd that the pressure sensor is located in the cabin. I would
have thought it would be closer to the purge valves, spliced in their lines
somewhere near. Might even be in the trunk area, not sure though. Glad
you got some use out of the diagram, pictures are worth a thousand
words for sure. Does the car shake and shimmy at idle? That would
also be a symptom of a vacuum leak. If she idles normally and you don't
have any oddities beyond the P -Code, might very well be non-operational
purge valve(s) due to a lack of stimulation pulses. Something to consider.

Good luck.
 

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Now we enter the Twighlight Zone. As I mentioned in an earlier post, there
was a significant change in the emissions system regarding the fuel vapor
management. In MY98 the cars began using a different style of vapor capture
and located the charcoal cannister in the left rear of the car. My car, MY97 has
a more simple and less efficient design and the cannister is located in the front left
wheel well, just aft of the tire. Everything I discussed earlier deals with my
car and I do not think your car's pressure sensor is like mine at all. So take
a step back and digest the attachments in this post. I think you will be able
to trouble shoot and actually locate your problem. Sorry for the
confusion and again, best of luck.

Paul
 

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It might be as simple as a faulty fuel cap seal. Wouldn't that be a kicker!
Let me know how this works out please.
 

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Discussion Starter · #7 ·
It might be as simple as a faulty fuel cap seal. Wouldn't that be a kicker!
Let me know how this works out please.
Heh, that very thought has been haunting me. I have another cap, I'll try that.

Regarding your second diagram, it's not clear at all where the left diagram is located in the car. The right diagram is clear, and is even labeled "left wheelhousing". So where's the left diagram located?
 

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Heh, that very thought has been haunting me. I have another cap, I'll try that.

Regarding your second diagram, it's not clear at all where the left diagram is located in the car. The right diagram is clear, and is even labeled "left wheelhousing". So where's the left diagram located?
Also left wheel housing.
 

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Discussion Starter · #9 ·
Ok, I just went out and measured my two gas caps. The one not on the car appears to be OEM, however the press-fit plastic cap used to remove the cap fell off, so it's non-functional. The aftermarket cap on the car goes on and off nicely. So I measured the distance of the gap from the retainer tang on both caps to the surface of the gasket. The aftermarket cap gap was slightly larger than the OEM, which may result in less of a seal. Since I can not use the OEM cap, I found some cork gasket material in one of my toolboxes, and fashioned a second gasket to go under the original rubber one, thus reducing the gap. Now the aftermarket cap does not spin on all the way and lock, but does seal very tightly. I'll give that a try for a bit.
 

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Discussion Starter · #10 ·
I pulled a plastic cover off the left wheel housing, and found where the B4/4 valve used to be. As you noted, the evap canister was moved after '98, so apparently, was the valve. :-(
IMG_5656.jpg
2703337
 

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Discussion Starter · #11 ·
Here's an interesting tidbit: on one of the diagrams you provided, it showed the fuel gauge with a "pressure sensor" on top of the assembly. My fuel gauge has not been working accurately, it doesn't show full when I fill the tank, and the readings vary wildly when the tank gets below 1/4. I just filled the tank for the first time since modifying my gas cap. Guess what? The tank read full for the first time in a long time. We'll see if it behaves better when below 1/4 tank. Meanwhile, 30 miles on the repair, and no CEL yet. Fingers crossed!
 

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I truly believe the issue is either close or very close to being resolved.
I removed the plastic cover on my car and took a photo of my pressure
sensor. Little tidbits like changing purge and cannister systems during
production runs are sometimes interesting as well as frustrating. It took
me a couple of long days and a lot of research to finally figure out what
I was working with. Even called the dealer, gave him my VIN and he
told me that I had the "ORVR" system, which is what you have. Very
wrong answer. You can see that a simple white splice and a couple of
Zip-Ties allowed me to clear my P-Codes and it has run fine since.
Hang in there.

MY97 SL 600 Purge Pressure Ssensor.jpg
 

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Discussion Starter · #13 ·
Well, 31 miles and another P1490. So I've eliminated the gas cap as a problem, there are no vacuum leaks from the canister forward, and the left side evap valve itself works fine. The right side valve at least holds vacuum. I think next I'm gonna T-in my vacuum gauge and see if I can monitor the operation between the valves and the canister. I also need to locate my B4/4 sensor. :-(
 

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Every now and then I get up and think "What If." First, I do not think you will find a B4/4 sensor
because the system change in MY98 did away with it. At least, I do not find it in any of the
diagrams associated with MY2000. That said, I took a long and hard look at your P1490
code and looked around for definitions and possible causes. Attached find the two Mercedes
code definition options for review on a P1490 code.

My 97's original issue had more than one code thrown, yours seems to have only one code, the
P1490. If you take a step back and focus on the two attachments, one thing comes to my mind
and that is purely this "Could the issue be a purge valve actuation issue only?" What if the
ECM was sensing a current consumption issue with one or the other purge valves? Assume
all the vacuum lines are good and no leaks exist for just a moment. You might get this code
if one or both the valves were acting up or something was amiss in the harnesses.

When I tore into my system and pulled the purge valves out for my bench testing, I noted that
the coil resistance of the valves was around 41 ohms each. Using ohm's law, I calculated that
the current flowing through each was just under the 300 ma limit. E=I times R, simply put,
the equation can be adjusted to : E/R = I or 12 volts/41 ohms = .29 amps, in spec so I
discounted a valve command problem.

It might be that your control module is sensing that one of the purge valves is not actuating
properly. It apparently has that capability, so maybe now it is time to look into the actual
verification that the valves are responding to the commands. You might verify the coil
resistances are somewhat close to one another and if they are, perhaps a harness wire
or plug contact doesn't have proper continuity. I am not wanting to throw a hand grenade
in the middle of your chase, but focusing solely on "Valve Actuation" might be worth a
thought since there are no obvious vacuum issues at hand. Perhaps a blast of some
good electrical contact cleaner in the connector plugs and valve contacts might help.
Just give the valve actuation idea a thought.
 

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Discussion Starter · #15 ·
I like the way you think! I will check the coil resistance and see where that's at. I'll also bench test the right valve and see if that one is working correctly.
If the B4/4 valve is no longer needed, how does the computer detect operation / failure?
I think I'd prefer an older car without computers. :-/
 

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Discussion Starter · #16 ·
I bench tested both valves. They both work as expected, drawing about 400 ma each. The docs you provided indicate they start working within 1 minute of start while the car is warm and idling, so I did that. The left valve began to vibrate about 120 Hz after 1 minute. The right perhaps does a little, but it's barely perceptible. With my voltmeter, I'm reading about 7.5 volts at the connector, which may be correct 12 volts DC at 120 Hz? I have an O-scope, maybe I need to hook that up? Anyway, 120 Hz seems too fast to actuate the solenoid. With a vacuum gauge on the other side of the engine (left valve) there was no indication of activity while the valve vibrated (although that was a T, maybe I should try without the T?) Any other thoughts?
Thanks for your help! I'm hoping this record may help others with the same issue in the future.
 

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Discussion Starter · #17 ·
Hmm, found something interesting. With the car running, and the left valve vibrating, I pulled the vacuum hose off the intake (vacuum) side of the valve at the throttle body. When I relieved the vacuum, the valve started clicking like crazy. When I returned the vacuum hose, it continued to click loudly. When I pulled and replaced it again, it went silent. So I got my old valve and reinstalled it. Now the valve clicked somewhat loudly.
With the vacuum gauge in place directly hooked to the canister side of the valve (no T), I could now read manifold vacuum. So the old valve is working as expected, and the NEW valve does not operate under vacuum (but is fine without vacuum?)

So then I tried the same test procedure on the right side. I could not get the right side to work with either the old (right) valve, or the new one (although the new one clicks like crazy when hooked to the connector with vacuum. The new one does not pass air, even when just blowing / sucking manually.)

I reinstalled the old (working) valve on the left side. I'm going to return the new faulty valve, and purchase an OEM replacement instead. Then I'll test and install that on the right side.

I suspect with only one valve actuating, there was not enough vacuum to make the evap system work. Both solenoids were working correctly from a voltage and amperage perspective, so that didn't trigger a fault, it was just the actuation was failing on the right side, so not enough vacuum.

So it looks like your suspicion of the actuation failure was 100% correct. Nicely done!

I'll let you know how I make out when the new valve arrives.
 

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Leave you unattended for a few hours and you figure it out. Good for you!
I hope the right-side valve replacement resolves the mystery P code. Some times
another set of eyes on the target helps. I am still curious as to what the purge
valve coil resistance is on the good valve and how it relates to the bad one.
400 ma is a bit high for a spec of 300 ma., IMO....Might not matter.

Just as a side note, when I bench tested my purge valves, they held a vacuum
for several minutes with vacuum applied to the arrow tip. They bled fairly quickly from
the other end when tested. FYI

As for the system determining what is going on without the B4/4, still looking into
that little issue. Might just be as simple as using the fuel tank pressure sensor or
the check valve on the cannister. Since it is the "New and Improved" emissions
process you can be it is far more complicated than the old pressure pulse measuring
and counting system of the first generation. If I ever get my hands on a clear "Theory
of Operation" on the ECM and its emission management, I will share it with you.
Do let me know how this valve replacement works out. Cheers.

Paul
 

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So you think you have some time off while you wait for the new part.
Well, take a look at the attachment and focus on the upper left area
and take note of : B4/3, B4/4, Y58/4 and the note at the end of all
that information. This is the answer to how your system actually
monitors the "Regeneration" or purging process and how my simple
purge valve system works. Someday I will get my arms around how
the two systems actually work, till then, this block diagram should give
you some peace of mind as to how the two systems differ. Fingers
crossed on the new valve fixing the error code.... Cheers

Paul
 

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Discussion Starter · #20 ·
Leave you unattended for a few hours and you figure it out. Good for you!
I hope the right-side valve replacement resolves the mystery P code. Some times
another set of eyes on the target helps. I am still curious as to what the purge
valve coil resistance is on the good valve and how it relates to the bad one.
400 ma is a bit high for a spec of 300 ma., IMO....Might not matter.

Just as a side note, when I bench tested my purge valves, they held a vacuum
for several minutes with vacuum applied to the arrow tip. They bled fairly quickly from
the other end when tested. FYI

As for the system determining what is going on without the B4/4, still looking into
that little issue. Might just be as simple as using the fuel tank pressure sensor or
the check valve on the cannister. Since it is the "New and Improved" emissions
process you can be it is far more complicated than the old pressure pulse measuring
and counting system of the first generation. If I ever get my hands on a clear "Theory
of Operation" on the ECM and its emission management, I will share it with you.
Do let me know how this valve replacement works out. Cheers.

Paul
Actually you figured it out, I just verified your theory.
For anyone reading this, keep in mind that all three valves (two old ones, one new) tested fine on the bench, and the valves worked as expected on and off. It was the operation of the valves at 120 Hz (or whatever it is) in the car where the valves no longer worked. The solenoids still appeared to work correctly to the computer, but the valves did not open and close at that frequency.
 
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