Diagnostic Tech: '97 Olds Cutlass Supreme (Originally posted July 22, 2008)

 Tuesday, July 22, 2008

Diagnostic Tech: '97 Olds Cutlass Supreme

This Olds Cutlass came in as a no-start. The customer tried to repair the car by replacing the ignition switch but when it still wouldn't start he had the car towed in. I found the battery dead and even if I didn't know someone had been working on the car it was pretty obvious when I opened the driver's door.

I guess the car owner didn't want to waste a lot of time putting things back together in case he had to scrap out the car (grin). You may think that an ignition switch is where the key goes but that is an ignition lock. The actual ignition switch is electrical and mounts to the top of the lower portion of the steering column. In the picture above it is left hanging below the brake pedal. Since the switch has been removed and only one bolt is left holding the steering column in place I can drop the column down and show you what you'll see in the switch mounting area with the switch removed.

The long metal rod is an actuator for the switch. When you turn the ignition lock back and forth the actuator moves back and forth. The end of the rod you see sticking up fits into a slot in the ignition switch. The ignition switch body fastens solidly to the column with two machine screws and when the actuator moves it causes the inner portion of the switch to move creating paths for voltage to operate the various electrical systems in key on, accessory and crank positions.

Since the switch is hanging there so handy I can insert a small screwdriver into the slot and operate the switch using the screwdriver as an actuator.

When I slide the switch to the crank position I should get ignition voltage to the yellow wire at the switch, and I do. But, I don't get starter engagement. The antitheft system on this car uses a small resistor pellet in the key. Even though I'm not using the key to actuate the ignition switch the key must be in the lock cylinder so that the theft deterrent module can read the pellet resistance. If the resistance isn't correct then the module won't enable the starter. The trouble here is that since I already know this I have the key in the lock cylinder and still have no starter engagement.

I have power at the yellow wire when the switch is in crank position. This power should show up at the starter relay fuse #11 in the fuse block. It does and the fuse is good. From the fuse the power should go to the transaxle range switch, through the switch in park or neutral to the theft deterrent relay. Now the theft deterrent relay and the theft deterrent module are accessible (just barely) if you remove the glove compartment. Feel around in the area directly above and you'll find them. There are metal screws to mount them in place. Now it could be that the car just needs a starter and the cranking voltage is reaching all the way to the solenoid. It could be that the range switch is bad and the voltage is never reaching the relay. What I'm going to do though is test the key resistance since all of this wiring is still laying there handy in the column area. If you look closely at the wiring coming from the steering column you will see what first appears to be a large orange wire but if you follow the wire to its connector at the lower end you will see that it is two small white wires covered by an orange sheath. Disconnect those two wires from the car harness and place your ohmmeter test leads on the column side of the harness. With the ignition key in the lock cylinder you should get a resistance reading that matches the resistance of the key pellet. You can measure the pellet resistance directly by placing a lead on each side of the pellet, one on one side of the key, one on the other.

This key pellet measured 1,100 ohms at the key but infinity at the wires. That means that either the lock cylinder isn't reading the key or there is an open in the wiring. Not reading the key can be a bad lock cylinder but it can also be a bad key with the pellet worn too badly to make good contact within the cylinder. There are 15 legitimate key codes, each with a different resistance range. When you take the key to your GM parts department they can place the key into a tester that will check the resistance and tell them the pellet code number. If it is the key that is not good it should show up while trying to read the pellet code. If you know the resistance you can tell the parts person the pellet code number even if the key doesn't read well enough for his tester to show it. There is a chart for this.

Now to verify that the antitheft system is the problem and to give you a better idea of where to find the theft deterrent relay I have removed the glove box and the metal screw mounting the relay so that the wiring can be accessed. The two yellow wires should be powered with the switch in the crank position. They are. The yellow/black wire should be grounded by the theft deterrent module to enable the starter. It is not being grounded because the module doesn't see the correct key pellet resistance.

You could jumper the big yellow wire to the big purple solenoid wire and the starter would engage with the switch or you could jumper a ground to the yellow/black wire and the starter would engage with the switch but the car wouldn't run because there is a fuel enable circuit as well. This is the point though where the rumors are true. If you know the resistance that the module is looking for you can place a resistor of that size in the car harness connector of the two small white wires and the system will allow fuel and starter to be enabled. Another interesting note, the modules are not programmed when new. Each new module will "burn" in to the first resistance measurement it sees on a crank and that will be what it looks for each time.

Since the goal here is a proper repair what I need to do next is remove the turn signal switch. With the turn signal switch out of the way I'll be able to see the two white wires at the lock cylinder. I expect to see one of them is broken. This is very common because the flexing of the wires while turning the key over the years eventually causes a wire to break. Sometimes the break will be inside the insulation and not seen but can be found by carefully pulling on the wires.

I won't go through the procedures for turn signal switch removal. They can be found in any good repair manual. You'll need a couple of special tools. One for removing the steering wheel and one for removing the steering wheel lock plate.

I didn't disconnect the turn signal wiring or airbag clockspring but pulled enough slack to get them out of the way. I can see the broken wire.

This lock cylinder will need to be replaced. I usually cut the connector off at the lower end and pull the wires up through the column. A trip to the friendly GM dealer gets me a new lock cylinder and key with good wiring and the proper resistor pellet.

To feed the wiring of the new lock cylinder down through the steering column I usually run a piece of mechanic's wire down through the column tube until it has several inches sticking out at the bottom. At the top, loop the metal wire to the lock cylinder wire connector, tape it all in place and pull the wire down through the steering column.

After that it is just a matter of putting everything back together. As a plus, the car even starts and runs now!

Kenneth Hayes

AKA Deranger

Diagnostic Tech: '02 Olds Aurora (originally posted Oct 22, 2007)

 Monday, October 22, 2007

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