I just got home and when I shut the car off the air pump stayed on. Is there a module or relay that controls this that sometimes fails? I went out about 5 mins later and it was still running. I had to disconnect the battery to shut it off. Has anyone else had the same problem? Car is a 1997 E320.

TIA,
Steve

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1997 E320
1990 Nissan 300ZX Twin Turbo (Stage X+)

My 1992 Buick Park Avenue did this. It was the result of slightly leaking air suspension. It did cut off after a while however. Strange, the car never did really sag in the rear. At one point, I removed the fuse from it and the car still set level- when there was no load in the trunk.

When you say "air pump", I am guessing you mean the pump for the suspension?

Good luck

Actually it is the air pump for the emission system.

Steve

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1997 E320
1990 Nissan 300ZX Twin Turbo (Stage X+)

Just unplug it, it's useless. Plug it back in for smog stuff.

i agree, as a temporary fix it can be unplugged, but the check engine light will come on, see the attached document, there is an electrical plug illustrated by the black arrow, pull the plug and it will go off. the relay that controls the air pump is the K40/4 which is located in the engine compartment module box on the passenger side, i believe the one that controls the air pump is a black cube type relay. if you find that the relay is causing the problems, let me know i have an extra one i will give you. if any information i have given you doesn't correspond to your car, give me the vin number and i will look at more specific information for your car.

I have the same problem with my smog pump. I have replaced the relay for it but it's like there's no power to it, yet the smog pump doesn't turn off unless my car is off. The new relay made no difference. Is there anywhere else i should check for the fix?

What year and model?

No power for the relay would equal air pump not running.

Hey MyCar,

On the 6Inline equipped cars it is a common problem, and I have discovered many cars in the junk yard here in the Sacramento Valley many have traces of repairs/part swaps/modifications, so it is a common problem.

The problem happened to me, and with my electronic component level experience.I found the driver transistor to the air pump on the engine computer shorted. On the 6Inline, it does not go to a buffer relay. I replaced the computer, and that is what it was..

Before you decide to replace the computer, You must not have the corroding engine wire harness, and on the 6Inline disconnect the connector to the airpump solenoid as both are actuated together, and they are in parallel in the same circuit. The air pump clutch must engage and disengage with 12v applied.

The reason i had the problem is the previous owner had replaced the airpump, and tinkered with all the vacuum plumbing responsible for the airpump, airpump solenoid, and egr solenoid.

Hope it helps,

Martin

Year matters, early cars has a belt driven AIR pump with a AC type clutch. Later cars ( 96? up ) have a full electric pump. The full electric pump has a 30 A fuse and a relay to control it. ( The computer triggers the relay )

Hello! i have not been on this site for quite some time. I decided to keep the smog pump unplugged for now on my s class. I am now deciding that I should tackle this problem will my smog pump. So from what I have found, there is no electrical connection to the smog pump relay switch so the new switch that I have added makes no difference. However, my pump still works when plugged in, and does not turn off if the car is running.
My car is a 95 S320, made in the late part of 1994, W140 inline 6.
Martin, I will try to do what you said about disconnecting the airpump solenoid and see what happens. It will probably wait till I figure out my other, new issue (no connection to this).

HeyMyCar,

I come to discover as their is no solenoid, and the smog pump is directly driven by the engine computer from active transistor like device-A true transistor has three pins. This device that drives the smog pump has a current sense leg that sends a logic-level condition to the microprocessor for current draw.

On my M104, the smog air pump driver transistor device was shorted. Someone on the web made some kind of little circuit to fool the computer with a operational amplifier (OP Amp as they are called). Cheap to build, to fool the check engine light...Interesting little circuit for us Californian's

Martin