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I’m posting this in the R230 forum even though the car is an SL55 AMG, hoping for a wider audience.
My problem is that when the engine is started using the key, the engine sometimes cranks but usually does not.
The car always starts normally when keyless go is used. This shows the starter battery, motor and relay are all fine. They have in any case been replaced, probably needlessly.
The results are the same with both keys, they unlock the car, can be turned in the ignition switch and when the engine starts, the transmission lever unlocks.
Monitoring what is going on at the starter relay, it is always energised when trying to start the car with the key but usually not for long enough to get the starter motor running, half a second or less.
If you think about it, the starter normally starts and continues to run until the engine is running and the starter motor is then killed. In this case, something is killing the starter motor before the engine is running but why the difference between the key and keyless go? The starter relay is actually under the control of the engine management computer, the key or keyless go button simply initiates the process...
A defective key switch assembly is a common problem in the R230's. Might be a poosible explanation. If the switch is defective, the car might think, you turned the key on and immediately turned it back off, then back on, erratically.
I’ve got the EIS (electronic ignition switch) out and apart and it’s a complex beast with three circuit boards linked by ribbon cables which fold around the key barrel. There are three micro switches and it’s possible one of these is not working but to get at it requires unsoldering. The EIS is coded to match the keys and also contains the odometer - with it removed, the odometer display show dashes. I’ve looked closely for bad solder joints because it is 17 years old but it looks fine.
It’s tough to work out what the main 10 wire interface is doing because 4 of those wires are the two CAN busses. So far as I can see, the start sequence is initiated by a CAN message sent to the engine management system. There doesn’t appear to be a wire which runs from the EIS directly to the starter relay, not surprising given the crank-until-running function and the parallel keyless go function.
The great issue is I understand you cannot order an EIS and return it if it turns out not be be the problem. It also costs many hundreds of dollars.
There are companies which claim to repair EISs but the ones I approached are more concerned with getting the EIS to recognise and unlock the key to allow it to be turned. No one I’ve asked has seen this problem.
I had a very different problem, but it might be related to what you are experiencing. From time to time my dashboard would turn into what is called here "Christmas tree" - every light would light up, but motor kept running. It would cure itself without any intervention. Then the problem disappeared. Never to be seen again. I figured that it is possible that some dirt/dust accumulated on the IR receiver on the EIS, so it would all of a sudden lose the key signal. This is pure speculation, but I suggest you try to clean the IR receiver. It might not help, but definitely is not going to hurt.
... I figured that it is possible that some dirt/dust accumulated on the IR receiver on the EIS, so it would all of a sudden lose the key signal. This is pure speculation, but I suggest you try to clean the IR receiver. It might not help, but definitely is not going to hurt.
I tried putting a piece of black PVC tape over the key window and that prevented the key from turning. The EIS correctly sensed a foreign key, so I think the IR communication is working though of course I have cleaned both the key and the EIS IR windows. I do not know whether the key keeps transmitting after being turned into the ignition-on position since it cannot be removed when it is and can only have got there by being a valid key, so the car knows that, by then, there is a valid key locked in position.
Mercedes are not keen to disclose the precise workings of the system - and the EIS wears a number of different hats. Either they just don’t know or else to explain it all in detail would compromise security. The last thing you want is for hackers to be able to get into the processors and reset the odometer or car thieves to be able to bypass the car’s security with a golden key.
I would use Star Diagnosis to see if the EIS is correctly reading the position of the key.
I think the EIS is correctly sensing the key position. I temporarily wired an LED across the coil of the starter relay (green, in the fusebox next to the starter battery) and the LED always flashes, even if only briefly, when the key is turned to start the engine. When the engine starts successfully, it’s on for a couple of seconds, when it doesn’t it’s on for much less time than that, and the starter motor makes a sort of grunting noise consistent with it being connected for just a short time. It’s then as if the starter battery is flat which of course it is not, because I can immediately start the engine with keyless go.
There are differences in DAS (Drive Authorization) between using the key in the EIS vs. KeylessGo. Using the key in the EIS is a two-way communication and the EIS actually re-writes a new random "secret code" to the key fob. KeylessGo is a one-way communication and uses a pre-programmed rolling code system (like garage door openers). When you press the start/stop button with KeylessGo, it simple shorts a wire that is fed directly into the EIS. At that point, the EIS does all the same things except for re-writing that secret code. I think the problem in this case is the EIS itself.
There are differences in DAS (Drive Authorization) between using the key in the EIS vs. KeylessGo. Using the key in the EIS is a two-way communication and the EIS actually re-writes a new random "secret code" to the key fob. KeylessGo is a one-way communication and uses a pre-programmed rolling code system (like garage door openers). When you press the start/stop button with KeylessGo, it simple shorts a wire that is fed directly into the EIS. At that point, the EIS does all the same things except for re-writing that secret code. I think the problem in this case is the EIS itself.
Thank you for that insight. I have a circuit diagram of the car and will look how the keyless go button in the gearshift connects to the EIS. That may in turn give some clues as to the differences between the two starting modes. It turns out the three-part circuit board in the EIS can be unfolded from around the key barrel by unsoldering 3 connections to the lock release solenoid and that will allow me to look more closely at the soldering.
I do not know whether the key keeps transmitting after being turned into the ignition-on position since it cannot be removed when it is and can only have got there by being a valid key, so the car knows that, by then, there is a valid key locked in position.
Since my problem occurred while car was running, I assume that EIS continues reading the key. Unless my problem was unrelated to key and EIS communication at all. Which is also possible. I never dug deep into it.
The EIS does continue to read a "heartbeat" from the key.
Rodney, you may recall an experiment I did two years ago whereby I removed the circuit board from the key with the engine running, and there was no consequence. This suggests to me that the EIS does not continue to read the key.
So it wasn't the RELAY in the engine? I'm sure I'll start the car up this week(been sitting over a month) and experience that hesitation on the first or 2nd start b4 it turns over
Rodney, you may recall an experiment I did two years ago whereby I removed the circuit board from the key with the engine running, and there was no consequence. This suggests to me that the EIS does not continue to read the key.
Was that on a KeylessGo car? I think those may work differently. On my W203 (no KeylessGo) a bad solder on the coil in the SmartKey caused it to die while driving and also caused the ICM to not come on when starting the engine. A quick re-solder of the bad connection and all was good.
I do know that there is a constant (or at least regular interval) handshake between the SmartKey and EIS. Maybe there is a provision where the engine will not be shut off if the key is "removed", but if there is a short in the coil that causes intermittent communication problems, that's when it shuts off the engine. DAS is a bit of a mystery. Even when I worked for MBZ, I tried learning more about it, but there is nothing beyond the basic things we can find on The Internet. It;s more closely guarded than The Colonel's Original Recipe.
I removed the EIS from the dash and took it apart. There are three circuit boards linked together folded around the key barrel. You can unsolder three connections for the solenoid which unlocks the barrel when a valid key is inserted to unfold the circuit boards. You can see the white infra-red transceiver in the centre that communicates with the the key and the optical sensor next to it which detects the position on the key barrel turned with the key. The key IR is fed through a light pipe to the the IR transceiver on the circuit board. On the bottom of the key barrel are white areas which the sensor uses to detect where the key has been turned to. Finally, there's the yellow leaf-spring microswitch which is activated when the key is turned, I believe to start the engine. I took it apart hoping to find bad solder connections after 17 years. I didn't find any and the behaviour - intermittent starting with the key - remains unchanged after I put it back together.
In the R230, the engine is started by a relay which is activated by the engine management computer. It initiates the start by switching on the relay and switches off the relay when it detects the engine is running. To do this, it monitors the crankshaft position sensor and once the engine is running above a certain speed, it is deemed to be running. In this way, the crank-till-started feature is implemented.
Since my car starts perfectly with keyless go but intermittently with the key, I was interested to see what the differences are. I used a Tektronix (top US manufacturer) digital storage oscilloscope to monitor the drive to the relay during the starting process. The blue trace shows the switched battery voltage to which the starter relay is connected and the yellow trace shows the other side of the relay coil which is grounded when the engine management computer wants to start the engine. So here is what happens when the engine is started using keyless go. The horizontal scale is 1 second per division, the vertical scale is 5 volts per division.
We start with the switched battery voltage (blue) and relay drive (yellow) close to 0 volts. After two seconds, I press the button on the shift lever; the switched 12v comes on and both traces jump. Then, the yellow trace drops back to 0 volts under control of the engine management computer; this switches on the relay and cranks the engine. After about one second, the relay is switched off as the engine management computer recognises the engine is running and both the blue and yellow traces increase in voltage as the alternator comes online. This is how it should be, all fine.
It's a smilar story when, on rare occasions, the key can be used to start the engine successfully. It seems to be more likely if the key is left in the "ignition on" position first for several tens of seconds, but it's far from predictable when you turn the key whether it is going to work.
In this case, I pause for about 2.5 seconds after switching on the ignition before turning the key further to start the engine. The starter motor is active for about 0.7 seconds and the alternator once again increases the battery voltage as it comes online.
So this is what happens when turning the key fails to start the engine. The starter relay is still energised but only for about 0.03 seconds which is not enough to get the starter motor running and the engine started. The engine management computer initiates the start but for whatever reason quits soon after. Presumably, the engine management computer thinks the engine is running when it is not, which points to a failing crankshaft position sensor though I cannot explain the difference in behaviour between a keyless go start and a key start. Two screen shots here. The first shows the very narrow starter pulse and the second shows this expanded. In all cases, the spikey transient when the relay is switched off is caused by the collapsing magnetic field of the relay.
Thank you. The service manual is clear that once initiated (via a message from the EIS to the engine management computer on the CAN bus), the start is under control of the engine management computer. For that reason, I think the (expensive) EIS is not the problem here. For some reason, the starter motor is being switched off because the engine management computer thinks the engine is running when it is not.
The crankshaft position sensor detects the position of the teeth in the starter flywheel and is used to detect engine RPM. As the teeth move past the sensor, an induced signal is used to measure the engine speed. As a backup, there is also a camshaft position sensor which determines the speed of the camshafts.
The next stage would be to attach my oscilloscope to the crankshaft position sensor to see what it is doing but it is very difficult to get at, as is the engine management computer which is under the driver's side fusebox. Unfortunately, I do not have a covered space to do it - the tests above were done in the open - freezing cold and pouring rain!!
The service manual is clear that once initiated (via a message from the EIS to the engine management computer on the CAN bus), the start is under control of the engine management computer. For that reason, I think the (expensive) EIS is not the problem here.
The EIS and engine controller both have control.
To stop a running engine you turn the ignition key from position 2 to position 1. That causes "circuit 15" to lose power. The same thing can happen with the key in position 2 if the EIS is faulty.
To stop a running engine you turn the ignition key from position 2 to position 1. That causes "circuit 15" to lose power. The same thing can happen with the key in position 2 if the EIS is faulty.
Thank you, I will look at that. The EIS is too complex for its own good and what I am trying to avoid is the significant non-refundable cost if I replace it and it turns out not to be the problem. When the key does start the car, it’s completely normal from then on. Maybe I should just use keyless go!
12-06-2019, 03:18 AM
