Check engine light

Sark,

Did you already try rebooting your car?

Barry

 

Its likely someone may have had this before - did you look to see if any other threads mention this code ?

 

Sark, are you hearing the secondary air pump running for the first 10 seconds or so after a cold start? It's hard to miss; sounds sorta like a Hoover vacuum cleaner on steroids.

I'm pretty sure it should only run from a stone cold start; its function is to inject fresh air into the exhaust stream to help the cats light off.

 

If it's not running on the first cold start, then you might check to see if the pump is fried.

You can disconnect the electrical connector from the pump, figure out which of the pins in the pump are + and -, then just jumper 12 volts straight into the pump to see if it runs OK. If it doesn't run with +12 coming straight into it, that may be your problem.

 

Sark if you want to verify take the connector that goes to the pump and check it with a multimeter. If your black wire in the connector (the car side, not the pump side) is continuous with ground then you can apply 12 volts to the red wire on the pump and ground the black side to verify the operation of the pump. These pumps suck, and often die. I had to replace one on my 360.

 

Sark, sorry for your trouble; I didn't mean for you to take the whole pump off the car. I just meant for you to disconnect the electrical connector, then make temporary jumpers to connect the pump to your battery to see if the pump works.

From what I remember, yes red is positive and black is negative. Just connect the battery to those two terminals with temporary jumper leads and see if the pump works.

Also, that filter may not be the best way to protect the inlet of the pump (mine had big gaps, as yours does) K&M make little crankcase breather filters that fit on the inlet side of these pumps very nicely. There are two sizes, 3/4" and 1", but I've forgotten which one I used - probably it was the 3/4"
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Sark, it might be the check valves leaking, but first check fuse 23 and Relay U in the diagram below. Those are supposed to be for the air pump.

Fuse 23 is also for the air horns, so an easy way to check if it's OK is to hit the horn button.
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Sark, first try to isolate the problem to either the controls or the valves, so just confirm that the pump runs when you first start the car with a cold engine. That'll tell you if the controls are working. You've heard the noise now with the pump on your bench, so you can't miss it when it runs; it sounds like a Hoover vacuum cleaner. Note, you'll probably only get one shot at this, as once the O2 sensors reach operating temperature, the ECU will not allow the pump to run.

If the pump doesn't run for 10 to 30 seconds with a cold engine then there's problems in the control system or harness. Assuming your harness is good, the other problems could be:

1. The O2 sensor heaters aren't working or are burnt out (possible)
2. The coolant temperature sensor isn't working, connector loose, etc. (not likely)
3. Internal fault in the Motronic ECU (not likely)

One point on the O2 sensors, and you may already know this; you can't have both closed loop AFR control with the O2 sensors, and air injection into the exhaust; the two are incompatible. So the air pump is only allowed to operate prior to the O2 sensors coming up to temperature, ie the first cold start of the day.

Many people are critical of the air injection system and would like to remove it, but as long as you have cats on your car, it's a very effective system that helps prolong the life of these outrageously expensive parts.

If the pump runs OK, we'll go to the next step of checking the solenoid valve, then the vacuum operated valves and finally the check valves on the exhaust manifolds.

 

Sark, you could check which terminal in the harness gets +12 when you turn the key on for first start of the day. However, it's probably similar to an injector and isn't polarity sensitive anyway.

 

Sark, next I would get one of those hand operated vacuum pumps, and pull a vacuum on the small line coming off the solenoid valve, going to the vacuum operated valves, and confirm they both work OK. These are the normally closed valves that open under vacuum and allow the output of the air pump to go to the check valves at the exhaust manifolds.

The last things in that circuit are the check valves themselves, and they're there to protect the vacuum operated valves & air pump from exhaust gases backfeeding from the manifolds. If you see some crud in the vacuum operated valves or their lines, and/or they may be stuck, then these check(s) on the manifold(s) are probably passing.

Back on the vacuum operated valves, I'm accustomed to seeing a vacuum storage reservoir in cars that use vacuum operated valves, and there may be issues with this leaking down, and not operating the vacuum operated valves. I don't know positively if our cars have one of these, but I'll probe around my engine bay and have a look.

Lastly, I think that if the O2 sensors do not come up to operating temperature via their heaters, and signal the Motronic to turn the pump off, and the Motronic has to do it itself via a timer, that could also set that OBD2 code that you're getting. So you might have some duff O2 sensors. Brian or another pro could confirm if it works this way or not.

Edit: We do have a vacuum reservoir; it's located just under the right side structural cross bracing in the engine bay, under the battery, but inboard. It looks somewhat like an A/C receiver/drier.