Low CAN voltage Mercedes e550 w211 -06

Hi

I have a weird problem. To begin with I cannot establish link to OBD port. I measured continuity on pin 4,5 to ground = all OK. I have good voltage on pin 16. Between Can high and can low (pin 6, 14 ) it's 70 ohm.

Here's what strange:
* CAN-HIGH pin 6 to 5 = 0,67 V
* CAN-LOW pin 14 to 5 = 0.4 V
(both with engine on/shut off)

Why is my readings so low. Anyone have an idea what I should check next?

/Lars

You are going to have chase down the high ressistance by disconnecting modules

Is my resistance ok? Worth mentioning I have ABS,ESP warning lights on dash. I quess I start disconnecting modules to brake-system First ( ABS unit, ESP Module)

70 ohms isn't perfect, but it's probably not enough to cause the kind of voltages you're seeing.

Do you have any continuity between 4/5 and 6 or 14? If no, that'd rule out a static short to ground.

From there, I'd keep disconnecting modules like Andy suggested.

I measured continuity between 4,5 and 6 = 197. Continuity between 4,5 and 14 was 86.
Is results in ohm ? Anyway what does this say?

Those readings represent a resistive (not direct) short to ground. Your CAN voltages are low because they're getting pulled low by a short, either in a module or in the wiring.

Any evidence of water intrusion? Because a water-logged module would certainly account for those readings.

I disconnected rear Sam main power Cable. Now I have 1,6 Volts (originally 0,6 v) On CAN_high and 0,6 volt CAN_low ( originally 0,4 volts)

I quess I must also disconnect can wires to this module.

1.6V on CAN-H and .6 on CAN-L is definitely better, but still being pulled to ground. I think you're on the right track with the rear SAM.

You might also consider what the rear SAM powers, and if you removed power to other modules/components when you disconnected that main cable.

Im not really getting smarter. I have attached a diagram(zip file) over the N93 (gateway module) which connects to X11/4 (DLC). Gateway talks to all modules.

I could lift the strip connector and measure (volt) each metal strip on the CAN distributor, And remove interconnect plug between the CAN distributors and at same time checking voltages on metal strips.

?

Hello, please lets start fresh. with all modules connected in the vehicle. ( stock ) please disconnect the battery negative terminal.

Measure resistance across pin 6 and 14, should be around 60 ohms plus or minus 10%

then measure from pin 6 to ground, and 14 to ground, you should have more than 500 ohms.

reconnect negative battery terminal.

turn meter on dc volts and measure voltage at pin 6 and ground
and measure voltage at pin 14 and ground.

voltage will change depending upon if the network is asleep or awake. please refer to this picture and compare voltages

DLC readings:

Battery disconnect:
Resistance across pin 6-14 = 60ohm
Resistance pin 6 to GND = 99 Ohm
Resistance pin 14 to GND = 41 Ohm

Voltage readings Pin 6 to GND :
in car closed Doors 5 min = 0,03V
When open Door = 0,68 V
Ignition on = 1,64 V

Voltage readings pin 14 to GND
In car closed Doors 5 min = 0,02 V
When open door = 0,35 V
Ignition on = 0,58 V

theoretically, shouldn't I get the same low readings if I measure directly on the Gateway. If so the gateway must be faulty I quess. I checked yesterday and I had constant 12v going in on N93

I fixed the issue now. To my gatewat there is two connectors. One connector is to the GPS unit. I removed this connection and I got 2.5 V idle on each CAN-L and CAN-H. And with ignition on - there was 3.5 V and 1.5 V. I manage to connect my scanner now.

I have 2 fault codes in ESP (Electronic Stability Program) which handles the ABS, ESP.
441a and 7284

Glad you are able to track down the problem. good job.