Perfecting multi stage diagnostic strategies


We have all faced cars that had multiple concerns that were interlocked together or seemed to be related. Sometimes creating one single complaint or sometimes creating multiple customer concerns. In our shop we find these types are jobs are going to have a positive outcome if you keep the customer well informed up front as to what you are doing, why you are doing it and how much it is costing them.

We recently had an opportunity to diagnose and repair a police car that had been retired because the trunk release did not work and the engine had a misfire that could not resolve. One of our customers bought the car from a government reseller and when they attempted to take it through Delaware vehicle emissions testing they discovered the MIL was inoperative.

The customer dropped the new to them 2009 Dodge Charger off and explained that they had failed Delaware emissions for no check engine light illumination, it was running rough and the truck would not pop remotely. A closer inspection of the car showed we indeed had a beat up Charger with a 5.7 Hemi and only 92,000 miles on the odometer. A glance inside the car showed a few interior panels were removed and there was part of a wiring harness falling down from the passenger side of the dash. A quick key cycle verified the MIL did not illuminate at key on engine off, though most other lights bulb checked as they should. The trunk release button was verified to not work and there was noticeable shake to the engine that went away above idle.

It is not uncommon for us to receive cars with multiple diagnostic concerns that may or may not be related, as a matter of operating procedure we sell an hour of testing up front for each concern. Once our testing is complete we will consolidate testing labor as we deem appropriate based on how concerns interlink. So in this case we sold 3.0 hours of testing up front. An hour for each perceived concern.

We started by going after the obvious electrical issue related to the MIL not working, our wiTECH quickly indicated the cluster had an active B2213 which is an internal fault detected code for the cluster. This code is known as the kiss of death on Chrysler modules but before we replaced it we decided to check power and grounds.

Pin #26 for power circuit A917 had a 10.0 volt drop indicating a significant point of high resistance somewhere in circuit A917. Poor voltage can cause false

Back probing the cluster carefully to verify power and grounds led us to a 10.0 volt drop on one of the power circuits.

internal module errors but it can also cause permanent damage that result in an internal fault code that will not clear. We are about 40 minutes into our testing and can see we will need to do some disassembly to prove out where the circuit was faulty. At this point we sold additional time to locate the point of high resistance with the understanding that the cluster may or may not still need to be replaced.

Subsequent testing showed a wire in the trunk near the battery and power distribution center that had been damaged at some point in its life and had grown corrosion. The corrosion had overcome approximately 1.5 inches of the wire increasing the diameter of the wire sheathing until it was ready to burst and was at least double the size it should have been. We cut the bad section out and installed a temporary jumper wire. The MIL still was not operational but now the trunk release function worked correctly, we believe the low voltage caused the cluster to fail internally. We permanently repaired the wire with solder and heat shrink. Once a new cluster was installed the MIL worked as it should. Because our testing for the MIL issue resolved the truck operation we did not charge a separate fee for trunk testing.

This wire had been damaged at some point, subsequently corrosion started to grow inside the sheathing, until it created a high resistance point.

Once we had our initial check done on the cluster we moved into our misfire diagnosis. Our trusty wiTECH showed A P0300, P0303 and P0306. A quick relative compression test with our Pico scope told us our issue was not going to be mechanical but rather would be found in the ignition or fuel delivery.

A quick scope of the ignition pattern showed us that we had high resistance likely because the plugs were worn. We removed the cylinder 3 and 6 coils to inspect the spark plugs and found 3 different type spark plugs between the two cylinders. Different brands and some were the correct resister type that was very worn and some were new fancy iridium plugs that typically do not work well in these engines. We stopped there and recommended a tune up with the correct OEM plugs because we felt further testing at this time would be wasteful and advised the customer a second hour of testing may be needed once the tune up was performed.

After the new plugs and boots were installed the engine was running very smooth except during a cold start, we noticed on a cold start the engine would misfire for 5-15 seconds.

16 resister type spark plugs are what this engine calls for, don’t put platinum or other fancy plugs in here as you may end up with undesirable results.

We removed the fuel rail with the injectors intact, to pressurize the rail, in order to prove what we thought may be a dripping injector. To our surprise the

16 resister type spark plugs are what this engine calls for, don’t put platinum or other fancy plugs in here as you may end up with undesirable results.

number 6 injector had a different color base that prompted us to look a little bit closer. We discovered the nozzle on the off color injector did not match the other injectors; the initial amount of fuel coming out of the injector at a cold start was different enough volume to cause this miniscule misfire. Installing a new injector completely resolved the remaining misfire counts at idle and the car subsequently aced its emissions testing.

Looking back we can see that someone tried to fix the misfire but ended up making it worse by installing incorrect spark plugs and the wrong injector. Once the bad parts were installed their diagnostic process likely stalled for them, likely causing them to think the issue was internal engine related. In cases like this, where there are multiple concerns going on, we break the problems down as small as possible. It is always easier to solve small problems than big ones. If you get the little problems resolved the big ones often evaporate anyhow.

Make sure when you are dealing with multiple issues like this you communicate to the vehicle owner clearly the multifaceted nature of the issues you will need to resolve. In our case we sold the spark plugs with the understanding that further testing may be necessary. Because we had clear and concise testing paths as well as clear results our customer didn’t blink an eye as we went through the testing and repair process. The end result was an easy testing session and a very happy customer.

An OEM injector should have 4 holes; this minor difference was enough to cause a cold start misfire
If you look carefully you will see 5 spray holes at the end of this aftermarket injector

Originally published in Auto Inc Magazine, a magazine geared towards independent repair facilities with the sole goal of improving the automotive trade.