A few years back, I was challenged by a 2013 VW Passat TDI (Figure 1) "no start" diagnostic that gave me a run for my money.
This vehicle has a particularly interesting story. It was involved in a fairly severe not-at-fault collision. The vehicle was without a doubt totaled. After doing a little research, the customer decided to buy back the vehicle from the insurance company. For those unfamiliar with total loss insurance claims, the insurance company offers a payment based on what the fair market value of the vehicle was pre-collision. If the owner accepts that payment the insurance company will take ownership of the vehicle and can then sell it with a salvage title to recoup some of the loss. The original owner has the option to “buy back” the vehicle for an agreed upon value in post-collision condition.
So, who would buy back a wrecked 2013 Passat? And why?
Diesel-gate
As it turns out, buy back wasn’t an unfamiliar term for this Passat as it was one of the vehicles involved in the VW diesel emissions scandal. As part of the "Diesel-gate" scandal settlement, VW agreed to either purchase the affected vehicles from the owners at agreed upon values, or offer a free fix and payouts to vehicle owners. The owner of this Passat had originally decided to keep the vehicle, but before taking the payout was involved in the collision.
For VW to buy back a vehicle, an appointment had to be made with a settlement ambassador at the dealership. The stipulations for the buyback were that the vehicle needed to be “operable under its own power” to qualify for the buy back. It was unclear if they would take the vehicle with a salvage title but the owner decided to take his chances.
The owner received a check for the agreed upon total loss value minus the buy back from the insurance company and what was still owed on the vehicle (and from what I’m told a healthy amount for injuries sustained in the collision). On top of all that, something got mixed up between the insurance company and the bank and after all of the dust settled the owner ended up with a clean title!
At this point, the vehicle is towed to our shop with the instructions to do whatever needed to be done to get the vehicle in a condition in which they could tow it close enough to the dealership that it could be driven on to the lot and turned in.
Building a buy back
Sometimes working on wrecked cars can be a nightmare, but something about assembling a vehicle by drilling holes in the hood and securing a brand-new radiator and condenser with industrial zip ties, per the customer’s request, sounds like something I would thoroughly enjoy. Unfortunately, my luck is nothing like this Passat owner’s so I had to watch from the next bay down as another technician got that ticket.
The repair mostly included suspension repair and replacement of the radiator, intercooler, and condenser assembly. If I remember correctly, the condenser was needed to support the radiator but it hadn’t been charged. There were a few damaged wires that were not repaired as most of them were for the headlights and turn signals.
Once the vehicle was returned to the customer a buy back appointment was scheduled with the dealership. On the day of the appointment, the customer went out to start the vehicle and found it as a "crank, no start."
If you caught any of my previous articles, you might already know that diesels aren’t my thing. What I don’t think I have previously mentioned is that I despise European vehicle diagnostics. So, while I didn’t get the Euro diesel ticket for the fun part of zip-tying the radiator on when it comes back as a no start, you better believe I get stuck with it!
After a considerable amount of complaining/sulking, I went out to crank the vehicle which seemed to turn over evenly but not start. I would be lying if I didn’t admit to spending an excessive amount of time visually inspecting wiring and components once we got the vehicle pushed in the bay. [one, two] It had left the shop running, and had only been sitting since it acted up. There were never any driveability issues during its first visit so it seemed to me that it had to be something external to the engine and related to the collision. After exhausting myself trying to determine what the cause could have been without actually having to do any dreaded Euro diesel diagnostics, I finally bit the bullet and got out the scan tool.
Using our Snap-On scanner, I found two codes (Figure 2) that reset: 4527-P0480 Cooling Fan Control Circuit 1: Electrical Malfunction – Cannot Be Tested At This Time; and 4096-P0016 Bank 1: CMP Sensor (G40) Engine Speed Sensor (G28): Incorrect Correlation.
Tackling the CMP DTC
Our scanner was correct when it showed “Cannot Be Tested” next to our cooling fan control code as a cooling fan had not been installed on this vehicle. The CMP/CKP correlation code looked like the code I needed to go after. I needed to get this dirty diesel back on the VW lot under its own power so I snipped the hood latch/radiator support zip ties, popped what was left of the hood up, and got to work (Figure 3).
The shop I was working for at the time did not have access to VW service information. Even now, Mitchell, ALLDATA and Identifix have no information on the P0016 code. Being in an aftermarket shop my entire career, I suppose I just assumed OE service information was unavailable to us. Now as a mobile tech that services the newest model vehicles that often aren’t covered by aftermarket SI, I know that the service information I needed was only a few clicks and $35 away. I could have also submitted an information request, but I decided to just take the code description and run with it as it seemed pretty self-explanatory.
Looking at data in the scan tool I was able to find PIDs for engine speed, crankshaft speed, and camshaft speed (Figure 4). They all seemed to read consistently but I did notice that the camshaft speed would read an RPM for a few seconds after the engine had stopped cranking (Figure 5). I decided that this was likely caused by a delayed refresh rate in the scan tool rather than something related to our no start.
This engine is a SOHC inline 4 cylinder. It determines the crankshaft position from a sensor (G40) located on the transmission side of the engine that reads from a reluctor on the crankshaft. The camshaft position is determined using a sensor (G28) under the timing cover that reads a reluctor on the back of the camshaft pulley.
With this information I had a list of potential causes:
Wiring issue – this made sense as I already knew the wiring was not in great shape on this vehicle. It was possible that something had shifted on that first cold crank and could be grounding out a circuit for the CKP or CMP. I was also able to see a speed signal from both sensors but the oddity in the CMP reading made me think that it was possible that the CMP reading could have been inferred rather than actual especially because a correlation code had set. While I might typically expect to see a circuit fault or sensor-specific code in the instance of a wiring fault, I decided not to rule this one out.
CKP or CMP sensor failure – While I might also expect to see sensor-specific codes with a failing sensor it seemed possible that a sensor could fail in such a way that it could produce a weak signal that would allow the correlation fault to set. Sensor failures can sometimes pop up after sitting for a while as this vehicle had.
Jumped timing – this made sense because the symptom wasn’t intermittent. It was running and once the symptom was present, it hadn’t started since. It didn’t make sense that the timing would jump either when it was shut off last or immediately when it was started after sitting. The engine did not have high mileage and if the timing belt had been loose, I might have expected it to jump timing during the collision rather than when sitting.
Broken timing belt – this was unlikely because the engine cranked over evenly.
Broken reluctor or damaged tooth – this could cause our no start and our correlation code however it didn’t seem likely because the symptom seemed to occur after sitting.
Engine damage that changed the clock position of the reluctor in relation to the crankshaft timing belt pulley (i.e. twisted or damaged crankshaft, broken dowel pin) – this was also unlikely as I would expect to see this symptom manifest with a running engine rather than while sitting.
I was leaning toward jumped timing or a wiring issue on this Passat. Looking for the next easiest test, I researched how to set up and check the camshaft timing and discovered that there were special tools involved that I did not have. None of the other techs had the tool and it wasn’t in our shop tools either.
Is there an alternative test?
After striking out with information on the P0016 code, I searched some of the forums for a known good CMP/CKP waveform and also had no luck. I decided to scope the CMP and CKP anyway hoping to find a signal that would indicate a broken wire I had missed in my visual inspection. What I ended up with was what looked to me like two good waveforms from the CMP and CKP sensors (Figure 6).
Using the bit of service information that I did have immediate access to, I was able to determine that to check the cam timing a special pin would need to be inserted into an alignment hole that passes through the camshaft pulley and into the head and would lock the pulley at TDC. With the camshaft locked, another tool would need to be used to lock the crankshaft pulley to the block. This tool locked the teeth of the crankshaft pulley with an alignment hole in the block. If the timing was correct the alignment marks on this tool would line up with marks on the pulley. When setting up the timing from scratch, there are further steps to adjust the camshaft pulley on the cam however I was not concerned about this because the locking bolts on the cam pulley were tight and I didn’t see any sign of them shifting.
I decided to do a Google search to look for an image of the crankshaft holding tool in use. The service information did not show the alignment marks of the tool very well but using the image I found I was pretty sure I would be able to tell if my timing was out without the tool. After aligning my cam sprocket up, I took a look at my crank and comparing it to the image I found it was obvious that the timing belt had jumped two teeth (Figure 7).
I was itching to take advantage of the fact that it was ok to skip proper repair procedures instead of just getting this junker running again. I jammed a bolt in between the pulley and belt and rolled the engine back to force the belt to jump backward. I had to perform this process twice to get the belt back two teeth. With the belt back where I needed it to be the engine fired right up and ran great. I hooked the scope back up and snagged a known good waveform for a 2013 Passat TDI. Printing them out on paper helped to visualize the jumped timing between the known good and bad waveforms (Figure 8).
Another pack of industrial zip ties had this thing back on its way to the dealership for a buyback.
Thinking back on this job, I used a few unpopular strategies to help me diagnose and repair this vehicle. It is often hammered into us that if we don’t have the correct tools or service information than we can’t fix the car. We're told that Google and YouTube have no place in professional auto repair. Realistically, it isn’t possible for an aftermarket all makes all models shop to have every tool for every vehicle that rolls in the bays.
I believe one of the best traits for an automotive technician is resourcefulness. I noticed this while paying attention to some of the more successful technicians I have had the opportunity of working with. When they hit a roadblock such as not having a tool or service information, they don't give up but instead, work around it. Keeping forward momentum is key and learning to leverage all available resources has drastically improved my diagnostic skillset.
