94 E320 won't start. Get codes 8, 22

[cotovelo]

Hello,

My 94 E320 wagon won't start at all. I read the codes and got 8 (coolant temp sensor: open or short circuit) and 22 (camshaft position sensor signal defective). This happened at night by a Walmart, and had it towed to my mechanic. I usually investigate before I take it to the mechanic, but this time I won't be able to have the time to do it. But I'd like to sound educated when the mechanic calls me up. Can anybody tell me if these codes are serious to fix? What are they? Is it something DYI to fix it? How much would it cost to fix them?

Thanks a lot in advance,

Carlos.
cotovelo@yahoo.com

I don't think either of your codes will keep the engine from starting, it will run like hell with the cam position sensor bad (tried that one before by unhooking it) but not starting at all is a mystery. Let us know what the final verdict is when your mechanic calls you

[jcyuhn]

I would think the cam position sensor is something of a problem. Without its input the engine electronics cannot determine which cylinder is (for example) at TDC on the compression stroke vs the exhaust stroke. I don't know how MB handles the loss of the cam sensor, but on a Ford I used to own the the software would guess at which cylinder(s) to fire. That engine also had a crank angle sensor, so it knew where the crank was in its rotation, but not which cylinder was on compression, exhaust, power, etc. If the car didn't start, you just stopped cranking the engine and tried again. Eventually the computer would guess right, and the engine would start and run fine. Does the m104 have any other method of determining crank rotation in order to time fuel injection and ignition? I own one, but I've never had to diagnose or fix any electrical/ignition problems.

- JimY

I found this description in ALLDATA that better explains what the sensors do. After reading it myself it appears the cam sensor will iindeed keep it from starting if it's bad.

READ ON!!!



Engine Speed, Crankshaft Position, Ignition Circuit Recognition
Information regarding engine speed, crankshaft position and ignition circuit recognition is transmitted from the crankshaft position sensor (L5) in the form of alternating voltage to the engine control module. A analog-to-digital converter transforms the alternating voltage signal into a square wave signal (TN-signal).

Engine speed is calculated by timing every half revolution of the crankshaft.

The crankshaft position is determined by voltage signals from the flex plate segment (A).




Recognition of ignition circuit 1 for cylinders 2 and 5 is transmitted by a permanent magnet on the segment (arrow).

The engine speed, crankshaft position and ignition circuit 1 recognition signals are required for the engine control module to perform the following functions:

* Fuel injection:
* minimum injected fuel quantity,
* start control,
* injector sequence synchronization,
* warm-up enrichment,
* acceleration enrichment,
* WOT (full load) enrichment,
* deceleration shut-off.
* Ignition:
* at start,
* during warm-up,
* at CTP (idle),
* at WOT (full load),
* at deceleration shut-off.
* Catalyst warm-up.
* Charcoal canister purging.
* Camshaft adjustment.
* Anti-knock control.
* Engine rpm limiter.
* Transmission overload protection.




Camshaft Position, Ignition TDC, Cylinder 1
The camshaft position sensor (L5/1) transmits an alternating voltage signal for every 20°rotation after TDC. This signal is converted into a square wave signal by the analog-to-digital converter and processed by the engine control module.

The camshaft position signal is required by the engine control module to perform the following functions:

* Fuel injection:
* injector sequence synchronization.
* Ignition:
* at start,
* fuel shut-off during ignition failure,
* anti-knock control.

Vehicle Speed Signal
The vehicle speed signal is transmitted from the ABS/ASR or ABS control module (N3O/1 or N30), to the electronic accelerator control module (N4/1) or the cruise control/idle speed control module (N4/3) and on to the engine control module (N3/4) via CAN.

The vehicle speed signal is required by the engine control module to perform the following functions:

* Fuel injection:
* deceleration shut-off.
* Engine rpm limiter.
* 2->3 upshift delay.
* Drive shaft - maximum rpm limitation.Engine Speed, Crankshaft Position, Ignition Circuit Recognition

[cotovelo]

Thanks for all the input. The mechanic has not called me up yet. I'll post the results so everyone in the forum know what happened.

Carlos.

[Kestas]

Or it could be bad wiring that goes to the cam position sensor.

[cotovelo]

i forgot to log this in. the problem was the starter.

carlos.