1998 Boxster Secondary Air Pump

[thstone]

Originally Posted by bagpiperse

I am new to working on cars, but it looks like the relay is not sending power to the pump. I read somewhere that there is an engine sensor that somehow activates the relay through the ECU (??).

One of the posts above references the engine temperature sensor. Remember that the ECU commands the SAI pump on at cold engine start. If the engine temp sensor is failed then the ECU might not ever think that the engine temp is cold and therefore, the ECU might never command the SAI pump on.

The engine temp sensor sends its signal directly to the ECU and the ECU commands on the SAI pump via a relay.

A relay is simply a component that allows a low power signal to send high power to a device. Relays allow most of the electrical system to be low power (and thus smaller and less costly). What this means is that when the ECU commands the SAI pump on, the ECU sends a low power signal to the relay which then sends (or relays) high power to the SAI pump.

To determine if this is indeed an "upstream" cause, check the temp sensor, ECU, relay, and associated wiring to ensure that they are all working properly.

[bagpiperse]

Thanks for those replies.

So, I think I left out some information. The secondary air pump is not coming on at cold start-up. It does work, as verified by giving it power directly from the battery.

I have checked the fuse and put a new relay in, and checked the wiring from the relay to the pump.

Thanks for the information regarding how the system works. I don't know where the engine temp sensor is to check it. I did some searching around on the internet, but didn't find anything saying where the sensor is or how to check it.

I don't know where the ECU is either, or how to check if it is sending the signal to the relay. Thanks again.

[thstone]

Originally Posted by bagpiperse

I don't know where the engine temp sensor is to check it. I did some searching around on the internet, but didn't find anything saying where the sensor is or how to check it.

Pelican Parts Tech Articles - Engine Sensor Replacement

Originally Posted by bagpiperse

I don't know where the ECU is either, or how to check if it is sending the signal to the relay. Thanks again.

The ECU is in the rear trunk. It mounts to the bulkhead between the trunk and the engine on the drivers side. Remove the lining and you'll see it.

You'll need a wiring diagram so you can find which pin outputs the signal to the SAI relay.

[bagpiperse]

Thanks, Thstone

There are many temp sensors on that link, but I am assuming that the temp sensor I need to check is the air intake temp sensor (as I am assuming that if the coolant temp sensor was bad, the temp gauge on the instrument panel wouldn't be working. Just my assumption though, as I am still reading and figuring things out).

Thanks again for the information on the ECU!

[bagpiperse]

Hi all,

So I could use some further guidance.

The secondary air pump is not receiving power at startup, and thus not running on startup.

I checked the pump itself and it runs off of battery power.

I checked the 40a maxifuse and it has conductivity.

I checked the connectivity from the relay to the connector at the pump and there is connectivity.

I replaced the relay.

I replaced the air intake (manifold) temperature sensor.

The pump still isn't getting power at startup.

Some have mentioned the ECU.

I have assumed that the coolant temperature sensor is not the problem, as the gauge on the dash seems to work fine. Please let me know if my assumption could be wrong. If not,

Is the only thing left to consider the ECU?

Thanks.

Scott