Foreign Service

Motor, Sep 2007 by Marinucci, Dan

Last month Dan introduced you to the electric air injection system found on many late-model VWs and Audis. This time he'll explain how to diagnose the system when it stops working as designed.

Last month I described the basic operation of the air injection system used on popular Volkswagen and Audi products. This electrically powered setup, which first appeared in the late 1990s, is still in use today. This montii I'll cover system diagnosis.

The most common reason to check tliis air injection system is the presence of DTC P0411. By the book, this trouble code means Secondary Air Injection System Low Flow or Incorrect Flow Detected. But in reality, this code could mean anything from a simple mechanical problem such as a leak to major electrical trouble. Sometimes, a failing system gives you a combination of both mechanical and electrical symptoms.

Always begin by verifying that the air injection pump runs. Let me repeat two important points from last month's column before I proceed: First, this pump runs for only 70 to 90 seconds after a cold start, so plan your test time accordingly. Second, the ECM controls a relay that's commonly labeled J299. This relay, in turn, controls current to the air injection pump.

There are several things you can try if the pump doesn't run after a cold start. Grabbing the proper scan tool is the easiest, fastest step. You see, some scan tools support VW's activated output tests, which enable you to energize actuators such as the J299 relay (screen capture in Fig. 1 below) and the N 112 relay, which I'll discuss later. If this output test turns on the air injection pump, it tells you that the pump, relay and related wiring are all good. It suggests that the ECM isn't getting the proper inputs from sensors such as the ECT and IAT. Does this vehicle have any other relevant symptoms and/or trouble codes?

Suppose the scan tool command won't turn on the air pump. Check the appropriate fuse and fusible link for the system first, then the J299 relay. Generally, the J299 relay doesn't cause much trouble on this system. But when in doubt, bypass the heavy-current contacts of the relay with an appropriate jumper wire. If the air injection pump runs, then the relay itself or the relay-to-ECM circuit has failed.

Of course, trying to operate the air pump directly with a pair of stout, fused jumper wires bypasses the ECM and all the related wiring. Remember that a normal pump draws 22 to 24 amps.

It's not uncommon to encounter a blown fusible link in the air pump motors power supply circuit. The most common cause of fusible link failure is excessive current draw due to a binding or seized pump motor, According to Jim Newkirk, a European vehicle diagnostic specialist at Identifix, it's not uncommon for moisture to accumulate inside these air injection pumps in colder climates. Newkirk explained that the moisture may cause premature pump bearing failure. In turn, failed bearings lead to motor dragging, binding and eventually a complete seizure. An air injection pump also will lock up if this moisture happens to freeze. Frozen moisture may even crack the pump housing.

Disconnect the nose from the air pump outlet and visually inspect the outlet port; rust inside indicates the presence of moisture. Or, turn on the pump for a moment with the outlet nose disconnected and see if it blows out water, Newkirk said.

Air Pump Noises

You may encounter two general types of air injection pump noises. One is an annoying rattle that occurs only when the pump is operating. An alert customer may describe a ratde that occurs for a brief time after a cold start and then disappears until the next cold start. This usually tells you that the air pump's rubber insulators, such as those shown in photo 1 on page 18, are broken.

The other condition is an air pump that either hisses or whisdes. An illuminated Check Engine light and DTC P0411 accompany these noises. These are the telltale sounds of a leaking air injection pump. The customer may confuse you by complaining that the engine sounds louder than normal. Indeed, an external leak does make this air injection pump louder than normal. But this clue may not be very helpful to technicians who aren't familiar with the sound of a healthy air pump. Furthermore, the customer may not clarify that this "loud noise" occurs only briefly after a cold start.

If the air pump is accessible, feel around it with your hand for air leaks while a helper operates the pump with fused jumpers or a scan tool. Or remove the pump and visually inspect it, especially the seam we're pointing to in photo 2. You may find a seal literally hanging out of this seam! As bad as this looks, this problem is usually very repairable.

I realize that it's your prerogative to either repair or replace certain parts. Also, some customers deserve and appreciate a break on a larger-ticket job. That said, one reason to fix this dislocated seal is that the repair is usually very reliable. Another reason is that, according to my homework, list price for a new OE air injection pump may range from less than 400 bucks to more than 800.