diagnostic tech 02 olds aurora

Diagnostic Tech: '02 Olds Aurora

A 2002 Oldsmobile Aurora was in recently with two complaints. The

headlights would dim intermittently and there was a Malfunction

Indicator Light (MIL/Check Engine Light) on. The car had the 3.5

engine and all the luxury features you would expect in any top of the

line automobile.

After spending some time trying to find a problem with the lights and

having no luck, I decided to move on to the MIL complaint and come

back to the lighting problem later. A lot of time can be spent

checking a system but when the complaint can't be verified it can

easily become time wasted. It's better to check for the cause of a

problem while the problem is present.

I pulled a P0410 trouble code from the car's engine control module.

A P0410 will set when the engine computer has commanded the AIR pump

on and the AIR valve solenoid open but does not see the O2 sensors go

lean as they should when extra air is being pumped into the exhaust.

"An AIR pump?", you ask. Yes, an AIR pump. The modern version of the

old belt driven smog pump is still alive if not well on many GM

vehicles. The AIR pump no longer needs a belt. It is an electric motor

and tucked away under the left front fender on the Aurora. The engine

computer will provide a ground to the pump motor for testing or for

normal system use. With a ground the motor should pump fresh air which

is piped to a vacuum controlled valve at each exhaust manifold. With

the vacuum control solenoid grounded by the ECM the vacuum will reach

each valve and open them, allowing the fresh air to enter the exhaust

and accelerate the catalyst operation. The fresh air entering the

exhaust as it is commanded should lower the O2 sensor voltage to a

lean condition. The lean condition should change the fuel trims. The

engine computer does monitor the voltage on the command wire to the

solenoid and will set a circuit electrical code if the voltage does

not match the command. This means that when you see a code P0410 as a

stand-alone code, you aren't likely to find an electrical problem.

One very common problem with the GM pumps is that the design of the

air intake hose allows water to be drawn into the pump housing. This

water will eventually cause the pump motor to be very hard to turn and

even freeze up. GM Technical Service Bulletin 02-06-04-024G contains

the related information. A replacement pump and an updated hose design

to prevent the water contamination are available as a kit. The part

number is 19515548. The original air intake hose filter is open to

road splash from water while driving.

The new design is covered on the inner fender side and open to the

engine compartment near the air filter housing. The install is fairly

easy. The air filter housing and inner fender liner must be removed

for access.

After finding the pump motor on this car to be water damaged and very

difficult to turn I replaced it and the hose with the update kit.

While looking for the GM TSB and part number I had noticed something

interesting. GM TSB 01-06-03-007A concerns headlamp and interior

lights dimming in cold weather. The bulletin states that a revised

alternator is available to fix complaints of headlamp dimming in cold

weather and perhaps the blower speed slowing or changing pitch

intermittently. The problem is due to intermittent low voltage. Engine

vibration may cause the alternator to lose field continuity and the

voltage regulator to reset. Now when the car owner dropped this Olds

off he did say that the alternator had been replaced at another shop

in an attempt to fix the light problem. I wasn't going to suggest yet

another replacement. What really caught my eye is that the bulletin

does go on to say that short term voltage drops with light flickers or

fluctuation is a normal condition with high electrical demand AND that

even after installing the revised alternator the car will exhibit

short voltage dips and headlamp dimming DUE TO THE AIR PUMP CYCLING.

Now just how much worse would this be if the air pump motor was water

damaged and near frozen, causing much more current draw? It looked

like the installation of the new air pump was going to help with the

light dimming problem.

As important as it is to verify a complaint before starting a

diagnostic job is verifying a repair after the work is performed.

After clearing the trouble code a short test drive was in order.

Everything appeared to work fine with no MIL on but a P0410 is a two

trip code. In other words, if the air pump failed the monitor test

during this test drive no code would be set and no MIL turned on. It

would take a second ignition cycle and test drive to set a code. The

air pump would need to fail the self test on two trips. To make things

move along better and get the most of the test drive I usually take a

scan tool along and record the ecm data.

A look at the scan tool data showed me that the air pump test had run

and had FAILED during the drive. I would have liked to include the

scan data capture in this article. You could clearly see the ecm

activate the pump and solenoid three times and three times see no lean

signal from the O2. It then gave up and logged a failure. Yes, I would

have truly liked to include that but I did a software update on that

scan tool earlier tonight not realizing it would clear the record

memory.

Back in the shop, I used the command function of the scan tool to

command the air pump on and verified the ecm could provide ground and

the pump was fully functional. If the pump was working as commanded

then the shut-off valves were the next place to check. Vacuum from the

intake manifold is piped to the vacuum solenoid. When the ecm grounds

the solenoid it opens, allowing manifold vacuum to reach the shut-off

valves. The vacuum should then open the valves allowing the fresh air

from the pump to reach the exhaust system. If the solenoid has an

electrical problem the ecm should detect that and set a related

solenoid circuit code. There was no circuit code so I used a simple

vacuum gauge to verify 18" of vacuum to the solenoid. With the engine

running and the vacuum gauge at one shut-off valve port I grounded the

solenoid and got only 5" vacuum. I blocked the other shut-off valve

port and tried it again. This time I had 18" of vacuum. The rear-most

(right side) shut-off valve was bad and losing vacuum. With the vacuum

loss, neither shut-off valve could open so no air from the pump was

reaching the exhaust.

I actually do have scan data on the test drive done after replacing

the shut-off valve. It was saved to the pc after being captured on a

different scan tool so escaped the fate of the first data capture.

You can see the O2 sensor go lean when the pump is on verifying the

system is operational.

I love my job!

Kenneth Hayes

aka Deranger

posted by Deranger at 11:26 PM

1 Comments:

Blogger Mike said...

I second Sir John's compliments!

Deranger, you have provided yet another example of what

a present-day Master Automotive Technician must do, know,

go through, research, examine, test, confirm, verify, repair,

re-test, etc ad nauseum...

You are a glowing example of what it "really takes" to fix

today's "little space shuttles" on wheels...

Folk don't realize that a DTC DOESN'T MEAN "replace this

part".

And they don't realize or appreciate the thousands of

dollars you have in training and test equipment.

Thanks again for yet another valuable post!

Mike.

PS. And thanks for the EXTRA effort you went through to

track, document and post this case!

3:26 PM EDT

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