Unfixable Dodge Magnum

For the most effective diagnostics, don’t just rely on the codes to troubleshoot. Actual testing will give you a bird’s-eye view.

Last issue, we talked about a problem created by technician error and made worse by hanging parts without knowing whether they would fix the concern. This time, I’m going to demonstrate another case study where a lack of tooling and training caused an otherwise competent tech to hang a few parts on a car that didn’t fix it.

MARAPR15_SMTF_BMW 15wu report

2005 Dodge Magnum RT

This issue’s subject car is a 2005 Dodge Magnum RT with the 5.7L Hemi and all-wheel-drive and about 106,000 miles on the odometer. It was brought in from a competent and reputable body shop about 15 miles away that we have worked with in the past. The shop’s owner informed me that the car runs OK but kept pitching a cam/crank sensor correlation code. He felt it “runs too good to be mechanical” so he figured it was electrical. He added, “If you ‘get on it’ from a stop, it doesn’t shift to second gear but shifts OK otherwise.”

Repair history is well known. The totally integrated power module (TIPM) was replaced five years previously during a collision repair. One year ago, the sunroof drains had plugged up and soaked the passenger floorboard, and the carpets were removed, dried then put back together. Since the check engine light illuminated, they have installed both cam and crank sensors (both OEM) with no change in the check-engine light or the shifting concern. He claims to have been fiddling with it going on a week or so and is out of ideas.

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We started out by hooking up our Chrysler wiTECH scan tool and looking at the module topology. A quick glace shows 17 modules communicating and only four do not have codes, stored or active, present. We notate the codes for future reference, but the two things that stand out are that the powertrain control module (PCM) has a P0016 active and the transmission control module (TCM) has zero codes. We will need to know that later, for now we attack the P0016!

Our service information indicated to us that most likely this was not going to be a circuit issue, so we suspect either our timing chain is not properly aligned or our PCM isn’t calculating correctly. A quick check of cam/crank difference parameter identification data (PID) showed -26 degrees. We would like to see this close to zero. After about seven minutes of testing time, we have our first supporting fact that our hunch is right. Time to dig a little deeper.

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We start by hooking our Pico 4425 up to the cam and crank sensor signal returns, as well as tap into cylinder one to measure pressure with our WPS500X pressure transducer. Our results show the cam and crank patterns are not lining up as they do when compared to a known good.

When reviewing our in-cylinder compression capture, you can pretty clearly see the exhaust valve is opening a bit too early and closing a bit too early. After about 25 minutes of total testing time, we are able to call this one a jumped timing chain. Our buddies at the body shop got sidetracked because they didn’t read through the code description and check theory of operation for what trips this particular code. Instead, they got caught up with the classic mistake of cam sensor and crank sensor being part of the code definition and thought the issue must be a bad sensor. While this sort of guessing will occasionally lead to a quick repair, the time lost by guessing can burn you pretty bad if you guess wrong.

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Our recommended course of action was to disassemble the front of the motor, identify the exact cause of the jumped chain and check for collateral damage. We called the customer and gave him his best and worst case scenarios with pricing and he gave the green light to proceed with a repair.

The transmission continued to have shifting concerns that were further diagnosed as internal hard-part component failures unrelated to the out-of-whack timing.  We advised the body shop to get the ignition wires replaced at their earliest convenience to prevent future drivability issues and that most of the modules had codes of some sort in them, so they shouldn’t be surprised if they stumbled upon them at some point.

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In this case the shop replaced the cam and crank sensors because they had a cam/crank-related code, not because actual test results pointed them toward these as bad parts. In fact, they did not do any actual testing at all, just a little bit of guessing. Remember, codes do not typically point to a bad part on a vehicle. The codes are there to help us determine which test should offer the greatest value towards an accurate solution. We still need to do the testing and understand the results.

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