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I recently started having some really strange issues at startup with my 2008 e320 diesel. I'll go to start it and all electronics will turn on but engine won't even try to turn over. I'll turn the key a couple more times, same thing. Then after 3-4 tries the engine will try to turn over and then stop. On the next try, the engine will turn over but the gear shift will lock and I'll get all of these error messages (see attached). I'll let it run for a few minutes and then all the errors will go away except for the "Safe Mode Inoperable" but I am able to shift gears and the car will run without any noticeable issues. Then I'll turn it off and turn it right back on and it will start just fine without any errors or issues. But, if I wait 10-15 minutes, I'm back to the beginning where the electronics will start but engine won't turn over. I can't get it into my local MB shop for a couple weeks so I was hoping someone here could shed light on this very strange issue.
It's very difficult to do any kind of online analysis. My first inclination would be to ensure battery and connections integrity.
Age of Battery
Load test battery
Check ALL high volt/amp connections to ensure they are clean and tight. This includes the battery terminals and BOTH opposite ends all the way to a chassis ground on the negative and all the way to the starter on the positive.
Make sure all other terminals on the starter are clean(ed) and tight, but don't break anything.
Be CAREFUL using a wrench on the starter positive terminal as an accidental touch to ground will cause a bad arc (spark)
No sense in going any farther without knowing these basics are good.
I can write a book on the safety components (Safe Mode Inoperable) but not until at least the basics above are all good.
If that simple stuff is all OK, then it gets tougher and tougher as now you have to start diagnosing components. The first place I would start is at the starter motor. It's too difficult to do this online. It gets down to a lot of "guessing".
On the "Safe Mode Inoperable" - let me try a brief primer. The faults showing up here MIGHT be isolated and a separate problem to the starting problem, but could also be related.
On the "SAFE" systems - ESP, ABS, any other traction control with which the car is equipped, there are some components that could fail, any ONE of which shuts the whole system down so nothing works. Because it is safety related, if system integrity is lost the system "suspends" until fixed. In the case of an "intermittent" like you seem to be seeing, some of the components that could fail can fail intermittently. If they do go on and off, every time they stop working the dash message appears, on a restart if they go back to working the dash message is extinguished.
The list of parts that commonly fail is not that big.
Wheel speed sensor (one at each wheel)
ABS unit.
Steering Yaw sensor
ECM/TCM
Low system voltage on startup, below the threshold voltage 11.8v (you claimed all is good here)
ANY one or more wheel sensors could fail intermittently or completely. Wheel sensors used a magnetic pickup with reluctor wheel. Sometimes wheel bearing grease can escape and contaminate the sensor making it intermittent or completely failed. Sometimes removing them and cleaning them could solve an appearing/disappearing dash message. Wheel sensor could also hard fail.
ABS unit can fail, so if it doesn't pass startup diagnostics, could be the problem.
A Yaw sensor on the steering could fail or fail intermittently same problem as it would shut the entire Safe Mode down while it wasn't reporting. OR, the yaw sensor could have lost calibration (comes sometimes if a curb is hit hard enough with one wheel. This is an easy solution to just reset the yaw sensor.
Finally, the ECM/TCM - the Safe Mode and all of its components rely on a completely functional powertrain, especially the drive by wire, many check engine lights will temporarily suspend Safe Mode. Safe Mode relies on the ECU controlling throttle so most failures that produce P-codes will suspend the safe mode. The program is designed to inform you via dash message NOT to rely on any parts of this system until the failure is found/fixed.
Hope some of this helps you, but beyond what I've shared I would only be wild guessing anymore.
09-15-2022, 12:39 PM
