A 2010 Mercedes Benz E350 4matic with 64K on the clock came in with a complaint of the right front headlight and blinker not working. We informed the Benz owner that it can be as simple as replacing the light bulb or clearing codes and in some cases, a module that controls the lighting may have to be coded, programmed or replaced. Now that the vehicle owner had a better understanding of why there was a diagnostic fee, we were able to begin our diagnosis.
If you’re not familiar with dealing with Mercedes-Benz vehicles you need an understanding of what we had to diagnosis to get the lights working again. Let’s start with the SAM (Signal Acquisition Module), and what it does, so if an MB comes into your shop you know what you are dealing with. The SAM module receives data from sensors, switches, and controllers, then send a command to activate components such as a light bulb. On this Benz, there are three SAM modules, two in the front, left and right along with another in the rear that controls different components. On this E350 the one we were concerned with is located at the right front footwell area next to the fuse box. The SAM module operates on a CAN B slower speed (Controller Area Network) BUS that exchanges information from switches, relays, horns, lights, heated seats, cooling circulation pump and more. Just like any other network on today’s vehicles if you change a component you may have to either code or program it on the BUS if you want it to work. Remember it’s not a matter of just replacing light bulbs anymore more, in this case, the SAM module had codes in it that were preventing the new bulbs from illuminating and operating as designed. The procedure entailed connecting a suitable scan tool that has the capabilities to clear and reset the SAM module. We decided to connect our AutoLogic scan tool to diagnose the problem and clear the codes for the lights to operate. Once the procedure was completed the lights worked and the message on the central display module on the dash was cleared.
Another lighting issue
On other Benz’s we have come across, the brake lights stayed on or were inoperative due to a defective rear SAM module. The fix on most of those MBs was ordering a new SAM, replacing it, followed by carrying out the SCN coding (programming) procedure. So, remember that if you come across a headlight, taillight, directional light, mirror or other component that does not operate after you replaced it, you most likely have to connect your scan to and check for codes, along with checking if the module needs to be coded or programmed. I suggest consulting service information such as Identifix, ALLDATA, ProDemand or MotoLogic so you can check for the most common issues and read up on system description to prevent wasting time and replacing parts that are not defective. Another good tip that I would like to share is what I do on any component that does not operate.
First, I connect a Power Probe to the battery and confirm that I have a good connection by taking the ground wire clip that is connected to the probe’s body and connect it to the tip. With the wire connected to the tip, the green led should be illuminated confirming you have continuity, but wait you’re not done testing that connection. Next, depress the power button and see if the 8-amp breaker pops. If the breaker pops, you have confirmed that you have a good power and ground connection. Now you can proceed to the next step of making sure you have power and ground to the component. With the key or power button in the off position, disconnect the wire connector from the component you want to test, then turn the power back on, check what side of the connector has power. The reason for the previous step is to make sure you connect the Power Probe’s power and ground to the correct side of the component that you want to check. If you don’t perform this step you may just burn out the component due to a diode that is installed in the component. Now it’s time to replace the headlight making sure the correct wattage bulb is used for the replacement. Volts times amps equal watts, why is this important? If you install the wrong wattage bulb such as a headlight, you can melt or burn up the headlight socket, wiring or lens housing.
To get the light operating again on this Benz E350 it was not simply replacing light bulbs or checking voltage and components, but using information learned or looked up in service information along with using a capable scan tool that was able to read and clear codes in the SAM module.
A GMC that refuses to start
Our next tough one was a 2014 GMC Acadia 3.6L with 49K (Figure 1) that was towed in as a no-start, no-crank. After speaking and questioning the vehicle owner we found out that there was nothing recently done to the vehicle and the same gas was in the vehicle as when it started before the no-start condition. During our questioning, we asked her if the vehicle had any dash lights illuminated or messages displayed at any time before this no-start condition. She relayed that there was some message on her dash display. After a few minutes of thinking, she replied that the message displayed on her dash stated something like “Service Side Detection System” now and then but thought nothing of it.
Well, that information was a good key to unlocking the no-start condition on this vehicle. Now, I can tell you if you’re thinking the no-crank/start is due to a battery, starter, fuel, spark, air or mechanical condition, you're dead wrong. Newer vehicles that we work on are different than vehicles of yesteryear. This vehicle is not your father’s Oldsmobile, Pontiac, Plymouth, Saturn or any other vehicle that is out of business, you’ll be out of business if you use the same old diagnostic approach. So, as you can gather from the previous sentence, you know that the problem is not related to any of the old normal systems or components. This is where using your brain, eyes, and hands comes in to play by using a scan tool to check for DTCs followed by looking up information on Identifix, iATN or other information systems.
The next step before replacing any component is to read a system description to help you get a better understanding of the system. We uncovered additional information on Google that stated there were problems with the Object Detection Module on many GMCs that the owner complained about. After reading that on Google we went back into Identifix and found a no-start condition from the left side detection module listed. Even though it was not an exact match for our B094C Right Side Object Detection Module, it was close enough.
Our next step was to make sure that there was no mud, snow, ice or other obstructions preventing the system from operating as designed. Checking for debris on the unit is an important step since this system uses a radar signal that is sent out to check for any obstructions. With no obstructions found we followed what Identifix had in their information about the system.
The system operates on the GM LAN low speed CAN system that communicates on the BUS. After checking for communication on the BUS we found that there was no signal and had to continue checking the system. The next step entailed locating the splice pack for the system which allows for module removal via the splice pack comb. When the comb is removed the modules no longer communicate on the BUS since they are disconnected. With the comb removed the vehicle communication returned, so we knew something was taking the BUS down.
When communication returned, it confirmed that the other modules that we disconnected one at a time were good and that there were no shorted wires. The only module that failed was the Right Side Object Detection Module, so we called the dealer and ordered a new one. After installing the new module, we programmed it so the BUS could be functional again. We followed all the regular procedures for programming that we have used many times before, such as using a battery maintainer and making sure that all the accessories were turned off along with doors, hood, and rear deck closed.
Once the module was programmed the vehicle started up, but the radio would not work. This was something that we don’t normally encounter as a problem. After we entered the radio data via the scan tool, we found that the VIN was not present and that the radio power mode was not switched to normal in the configuration information. We typed in the VIN and changed the configuration to normal and the radio came back to life. The customer asked us to program in all her AM, FM and Sirius channels (Figure 2) which we did and then returned a running GMC to her.
A misplaced shift?
A 2005 Chrysler Town and Country 3.3L with 90K came in with a P0305 Cylinder Misfire, P0700 Transmission Fault and P1776 Solenoid Switch Valve Latched in LR Position. We did our due diligence and found a TSB 21-001-13 that deals with a solenoid that is located in the valve body and not in the solenoid pack where all the others are located. The issue deals with the manual valve in the transmission not in the OD position that sets the DTC. The TSB suggests that the shifter adjustment be checked and adjusted if needed. We also checked to make sure that there was no debris in the transmission fluid. Our next step was to follow the TSB and recommend that the transmission controller be reprogrammed with the updated file that Chrysler suggested for this DTC. Since this vehicle owner was on the fence about keeping this vehicle, he decided not to perform any repairs and traded the vehicle in. The takeaway from this vehicle is if we did not check TSB’s we would have not known there was an update and possible suggested a different path of repair.
Does it need a "flash?"
A 2007 Toyota Tundra 5.7L with 159K (Figure 3) was towed in from a used car dealer with a no-start complaint. Anytime we get a vehicle from this particular used car dealer they always think that reprogramming is the issue that is going to fix the problem. As we proceeded to check the vehicle out, we noticed that the VSV and Traction Control lights on the dash were illuminated. We had seen this before on another Tundra that was running that had the same dash lights illuminated and was stuck in low gear. This Toyota was a no-start, but the two Tundras may have something in common. We called the used car dealer and told them that reprogramming was not going to solve the no-start condition on the Tundra. We requested two hours of diagnostic time to locate the no-start issue on this vehicle.
One they approved the two hours we connected the Toyota Techstream scan tool and received a message that stated "waiting for an acknowledgment." As we started to check the vehicle out, we found a communication issue, so we performed a CAN ohm meter test that provides a 63 Ohm reading (Figure 4) that indicated no problem.
The next step was connecting a labscope to diagnosis and check for communication packets on the BUS. We made sure power and ground were good then moved on checking the 5-volt reference signal. The results of that test displayed no 5-volt reference, so we started unplugging all 5-volt reference signals to see if the communication (Figure 5, 6, and 7) would restart, but no luck. This meant that something else was pulling down the 5-volt reference, which indicated something had to be shorted.
We located a comb for the BUS that was located under the glove box that allowed us to disconnect modules. Bill decided to unplug each connection one by one to see if there was any change, unfortunately, nothing did. Bill called me out to the parking lot where the truck was parked and asked me to check the vehicle with him. As Bill proceeded to show me all the tests he performed, I remembered that I had encountered another Toyota that had a similar problem. I made mention at the beginning of this case study that the other Toyota also had the same lights illuminated on the dash, but that truck started. I recalled what the issues were on that truck which led me to go out under the hood and locating the AIR system.
My next step was to disconnect the 12-volt wire (Figure 8) that goes to the solenoid, then have Bill crank it over. Bingo, the engine started right up, and the 5-volt signal returned along with all the other systems up and running. But what caused the solenoid to short out?
Well, this is nothing new to me or anyone who worked on AIR emission systems. Usually, the problem is that the check valve diaphragm is burnt out, causing hot exhaust gases to get through to the solenoid, melting it and causing it to short out. This was indeed the cause of the no-start and the 5-volt being pulled to ground. We suggested that both check valves on the system be replaced along with the Bank 2 shorted solenoid. The used car guy decided just to leave it unplugged and sell the vehicle as-is. You can’t fix stupid!
Finishing up with a Porsche
Our last problem vehicle is a 2004 Porsche Cayenne with a 4.5L V8 with 145K on the clock that was towed in as a no-start. Our starting line on this vehicle was speaking to the vehicle owner who was not forthcoming with any helpful information.
We started with the heart of the electrical system and found that the battery only had 4 volts present. My tech Bill proceeded to charge the battery up then checked for voltage at the battery jump start post only to find a reading of 0 volts. Bill then moved on to check if there was any voltage at the fuses under the hood, once again only to find the same results of no voltage.
Researching in Identifix and iATN came up empty so we had to follow the electrical trail that leads to the battery and a reset circuit breaker. Bill continued to check the vehicle out and found that the left front height sensor that is located on the control arm (Figure 9), had a broken connector and corroded connecting pins. The owner refused to repair this issue and just wanted the vehicle to start. We installed a new battery and reset the circuit breaker (Figure 10), checked the charging system and invoiced the customer.
I hope these case studies help you get a better understanding of some of the systems allowing you to check them and helps you diagnose and repair them faster.
