You may recall not too long ago a post I made regarding a CEL and ensuing repair to the PCV hose that was creating a massive vacuum leak.  Well my CEL-free driving didn’t last forever.  About a month or so ago I started getting a P0442 code, which is an indication of a small leak in the evaporative emissions control system.  In other words, I had a leak somewhere in the myriad of plumbing that comprise the emissions system on a modern car.  I would clear the code using my OBDLink MX Bluetooth reader and the Torque app on my Android phone, but it would always return in 50 or so miles.

This type of fault isn’t the end of the world, as the car will still run just fine, but you wouldn’t pass a smog inspection (not required where I live.)  So I let it go until I had time to really track down the problem.  A short time after this first code, I started getting another CEL, this time for a P0161 fault.  This fault is for the O2 Sensor Heater Circuit (Bank 2, Sensor 2).  In other words, the post catalytic converter on the second (right hand) pipe.

Again, neither fault would severely affect performance, so I let it ride and even attended a track day with the CEL blaring in my face.  After returning from Road Atlanta, I put the car back up on jack stands to swap out the PFC 08 race pads for something more street friendly, giving me the opportunity to take care of the two emissions related problems.

Parts Diagram of O2 SensorsI had already ordered up a new O2 sensor, as it was almost a guarantee that I’d need a new one.  Now you could order the OEM part (# 11781427884) for $190+ or you could get the NGK equivalent for about $64, I opted for the NGK.  NGK is an OE supplier, especially to the Japanese autos, and I’ve had good results using their products on my MR2 Spyder.

Fortunately both secondary (rear) O2 sensors on the E36M3 are identical, so if you want spares it’s not too difficult to have just one on hand.  While the car was up in the air, I also noticed that the plastic cover that goes over the O2 sensor wires was broken, a result of unloading the car off the trailer on an incline.  Fortunately that part (11781427639) was inexpensive and another easy replacement.

Once under the car, I quickly saw what the issue was.  The O2 sensor wires had been resting directly on top of the hot exhaust pipes, which had melted away the insulation and causing either a continuity issue or simply shorting the circuit.

Chaffed O2 Sensor Wiring Broken O2 Wire Cover

The new O2 sensor comes pre-lubed with anti-seize and crush washers already installed, simply unscrew the old one and screw in the new one.  It comes with instructions on how to properly torque (usually finger tight then 1/2-3/4 turn.)  This time I made sure to properly twist the pig tail as to keep it from contacting the hot pipes.  Job done.

Now onto the more difficult task of finding the “small evap leak.”  This could potentially be a needle in a haystack type situation, as there are just so many possibilities of where a leak (especially a small one) could originate.  It could be a rubbed hose or a split in a plastic tank or even a loose gas cap.  In fact, the gas cap is where I started.  It’s often the most likely culprit.  Mine was nice and tight, but it was also 16+ years old, so I opted to replace it (PN 16111184718).  Unfortunately this didn’t solve my problem, so time to dig deeper.

A professional mechanic might use a smoke machine to find the leak, and I even contemplated making a DIY version to smoke the system.  Like the name implies, you are simply filling the fuel system’s ullage with smoke.  What’s ullage you ask?  It’s the open, unused space in a container, such as a fuel tank.  One of those terms you learn in flight school and as a maintenance test pilot.

If there is a leak in the system, then the smoke will escape and can be seen with flash lights and careful searching.  Make a YouTube search for evap or emissions system smoking for examples.

Since I didn’t have a proper smoke machine on hand and didn’t really feel motivated enough to build one from scratch, I decided to see if I could find common sources for a small evap leak in the E36 (or BMWs in general) chassis.  As it turns out, this type of fault is fairly common on aging E36’s, and is almost always a leak associated with the fuel expansion tank (not to be confused with the coolant system expansion tank).  I decided to check mine in hopes of visually finding the leak.

Expansion Tank Part Diagram

In the part diagram above, the expansion tank is labeled #1.  It’s located in the right rear wheel well, directly above and behind the plastic inner wheel well liner.  With the right rear wheel removed, it is very easy to access.  There are just two plastic nuts and one plastic push rivet holding the liner in place.  Remove the liner and you’ll be able to easily see the expansion tank.

Expansion Tank Mounted

I took a good look at the plastic drain nipple on the bottom of the tank, as they are known to crack.  Fortunately mine was in good condition, so now I had to take a look at the two on top.  In order to gain access, the tank must be removed.  To make life a little easier, unmount the fuel filler neck and move it out of the way.  There is one plastic nut at the low point of the plastic neck, one more towards the top, and one metal nut near the filler.

You’ll also want to pop out the rubber boot that goes around the filler.  It should easily deform and allow you to pull it out.  Once out you can get a better view of the top of the expansion tank and the pressure sensor that’s attached to it.

Removing Rubber Boot from Fuel Filler Open Fuel Filler

Now the most difficult part of the whole removal: the OEM hose clamps.  BMW used some one-time use crush type clamps that are damn near impossible to remove.  Rather than try… okay I tried a bit, I’d recommend just snipping off the hose as close to the nipples as possible, as to leave yourself as much hose to work with later on.  The bottom drain hose will have to be sacrificed, as it is so short that it can’t be saved.

With the bottom drain hose snipped, I removed the final plastic nut holding the tank to the body.  I could then lower it down to check the top nipples.  And just like I thought might be the case, the top large nipple was cracked.  There was my leak!

Cracked Hose Nipple

With the tank dropped down, I snipped the two remaining hoses.  Then popped off the pressure sensor from its mounting base on the rear of the tank.  Now the tank is completely free.  I moved it over to the bench, where I gave it a good scrubbing to remove the 16 years of road grime.

The nipple in question had broken right where the inner metal reinforcement had stopped.  Essentially the manufacturer hadn’t run this short piece of brass tube far enough up into the outer plastic nipple, creating a point of weakness.  It’s no wonder why so many have broken in this exact same place.

Broken Expansion Tank Cleaned Expansion Tank

Now I could order a brand new expansion tank (PN 16131183056) for about $75, but it would have the same inherent weak point.  What I needed to do was reinforce the nipple further inward.  I measured the existing metal tube at 6mm, just under 1/4″ (6.35mm).  You’d have a hard time finding a piece of 6mm brass tube at the local parts store, but I was able to find a short piece of 1/4″ copper/nickle alloy brake line that might just do the trick.

I measured out the brake line so that it would run nearly the entire length of the plastic nipple and base, but allow just enough clearance for the gas to flow properly.  I cut the line with a fine tooth hack saw (a line cutter probably would have worked better) and filed the burs smooth.  I needed to open up the plastic by 0.35mm to allow the 1/4″ tube to fit, so a little work with the drill took care of that.

Drilling Out for Clearance Measuring Off New Copper Line Prior to Installing Nipple Copper Nickle Brake Line & OE Brass Tube

Now to secure this new reinforcement and make sure it remains sealed.  At first I tried some two part epoxy specifically made for plastics.  Unfortunately it didn’t adhere well at all.  After curing, I wiggled the nipple a bit to see if it had held and the epoxy immediately lifted up from the black plastic.  I scrapped off the offending epoxy, scuffed everything with some sandpaper, cleaned it with some acetone, and then went with old faithful: JB Weld.  I used the quick setting variety, which seems to worked like a charm.  It adhered better and remained slightly flexible.

JB Weld Repair to Expansion Tank Repaired Expansion Tank

While I was picking up the short piece of 1/4″ brake line at the local NAPA, I also picked up a foot of 3/16″ fuel line and four small screw (worm) clamps.  As mentioned previously, I cut away the OEM clamps and a short amount of hose in order to remove the tank.

With the JB Weld cured, I loosely placed the expansion tank back into the wheel well, resting on top of the brake rotor.  First connect the two rubber lines.  You shouldn’t get these mixed up, as there are two different sizes (~1/4″ & 3/16″ in SAE) for the two different sized nipples.  There was still plenty of hose length even after trimming a bit off during removal.  Slip the hoses on and tighten down the clamps.  The pressure sensor also needs to be reattached to its mount on the rear of the tank.  Make sure its plug doesn’t pop off, it’s easy to do.

Repaired Expansion Tank Reconnected

With the hoses reconnected and the sensor reattached, the tank can go back in place, secured with a plastic nut.  The fuel filler neck (which was pushed down and out of the way) can also be worked back into position and secured with the three nuts (two plastic, one metal.)

Now reattach the lower drain.  The original short hose has been cut and is too short to be of any use.  The foot of fuel line I picked up at the parts store will go here, along with two new screw clamps.  Make sure to keep it out of the way of any other clamps that might chaff the hose.

Expansion Tank Drain Reconnected Expansion Tank Mounted

Almost done, just need to install the wheel well plastic liner with the two plastic nuts and one push rivet.  Finally I hooked up my OBD reader and cleared the codes.

The results: the following day I took the car on a 250 mile trip with no CEL and no other issues.  If your E36 is experiencing a P0442 “Evaporative Emission Control System Leak Detected (small leak)”, I highly recommend you take a look at your fuel system expansion tank.  It’s a cheap fix with just a little work, and you should end up with a far more robust solution than just replacing the tank.


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