Intermittant Power to the AIR Pump

[todd8]

Been having a problem with intermittant power to the connector to the AIR pump on a 1999 SL2 with 157K.

- Have verified that the pump works just fine by connecting it directly to a
12 v source.
- Have removed and cleaned all grounds to the chassis
- Have verified proper operation of the AIR Relay and even swapped it out
with a known working relay
- Have verified that there are no blown fuses

At this point I am at my wits end trying to determine why this connector sometimes receives power and other times it does not. (It is understood that this pump is energized for 45 to 60 seconds upon cold start up and that is when the power is intermittant - didn't want to give the impression that I thought the pump was supposed to run continuously)

In any case, if anyone has any ideas of what could be causing this issue or what else I should check, I'd apprecaite it.

[OldNuc]

Need to inspect the connectors under the UHJB and at the pump. There are several possible points of fail. Black 1 way connector at rear end of UHJB close to the green maxi fuses. Gray 68 way pin D-10 and pin F-11 under the UHJB, and the connector at the Air Pump.

To get under the UHJB there are 2 or 3 small bolts that hold the flange down to the body, you can see them with the cover on the UHJB, do not take the bolts out of the fuse side of the UHJB that is under the cover. Before working on this disconnect the battery negative at the battery and disconnect the red wire at the UHJB.

Look at each connector in turn for any signs of loose connection or overheating. I would suspect the connector at the blower as the more likely point of problem.

[todd8]

Thanks! Will check the connections at the UHJB as soon as it warms up a bit. Currently 7 degrees outside. I did check the connection at the pump and it appeared to be fine.

[OldNuc]

There are several points for failure including the big green AIR fuse so pull it out and look for cracked element. The single wire black connector is also right close to that fuse.

[todd8]

Followed your instructions but found no corroded or loose connections. Verified continuity between the uhjb and the power connector to the pump. again verified pump runs when connected directly to the 12 v source. Verified fuses were all OK as was the relay. Even switched out fuse and relay with others, no dice.

Are there any other sensors, etc. that control power to this circuit that could have failed?

[OldNuc]

Exactly how is this problem showing up? There are irritating quirks in this system that can end up starting and stopping the air pump. If you have checked the electrical out then you might be having one of these irritating features of this system.

[todd8]

The problem started with the pump not running maybe once out of every five starts. It progressed to the point where now the pump might run once out of every ten or fifteen starts. Have had no blown fuses and the tubes and ports go the exhaust are clear. After the problem started I cleaned all grounds, but no luck. I haven't noticed any patterns preceeding when the pump does run.....am stumped

[OldNuc]

Where are you located?

AIR system operation.

PCM monitors the following to control air system
ECTS
IAT
MAP
Front O2 sensor

Air pump disabled when:
DTC set, P410, MAP, TPS, EGR, O2 sensor, Misfire, or Fuel trim (171-172)

Fuel System in Closed Loop
Air Pump On >60 seconds
RPM >3200
MAP less than 20kPa
Battery less than 11v
Air Flow (calculated) >30 g/s
ECTS <40F or >174F

Clean the PCM power ground located on the front upper trans mounting stud.


Does it set a P410 when it does not run?

[todd8]

located in NE Pennsylvania....has been very cold lately, so the pump should be running. Haven't had the code set in about a week, but will try cleaning that pcm ground.

Thanks for continuing to help

[OldNuc]

It will not run if the temp is below 40F. What can happen is the ECTS is over the 40F and you fail the prestart sensor check for temperature between the ECTS/IAT/TTS if automatic and when you start the car and when the car starts the ECTS goes below the 40F the pump shuts off. As long as you are in open loop which is about 15 to 30 seconds depending the system will start and stop on temperature. It is a really rough design on the programming ... Turn key to ON but not crank and look at the temp values on those 3 sensors and see if they are all within 5C.

[todd8]

Thanks for that information. Will give it a try and report back....

[OldNuc]

This system was conceived in a back ally somewhere and is a real pain when it wants to be one. Just for a quick check disconnect the solenoid valve that supplies vacuum to the diverter valve and then check the coil resistance to ground on the highest resistance range, 1 probe on the block and the other on either solenoid connection pins. Should read as an open circuit or very high resistance value.