1999 CLK 320 Mercedes Benz- getting a oxygen sensor preheat circuit malfunction code on all 4 O2 sensors. Got to think it is a relay, fuse or? Hard to believe all 4 sensors would go at the same time. Any ideas on where to start looking as I do not have a repair manual for this car? Thanks in advance!

More details required pls.

The code means that there is a problem with the heater element circuit of the heated oxygen sensor. Water getting inside the heated oxygen sensor connector can caused the heated oxygen sensor fuse to blow, which is a very common problem for this type codes. Before replacing the sensor, check for the condition of the heated oxygen sensor fuse and connectors.

code p0050 refers to heated oxygen sensor (HO2S) 1 bank 2 heater control ---circuit malfunction===causes --wiring---HO2S ---ECM
replace the sensor in the exhaust pipe and the code should clear

P1491 Rad Fan Control Relay Circuit An open or shorted condition detected in the radiator fan control relay control circuit. This includes PWM solid state relays.P1495 Leak Detection Pump Solenoid Circuit An open or shorted condition detected in the Leak Detection Pump (LDP) solenoid circuit.P0753 (M) Trans 3-4 Shift Sol/Trans Relay Circuits An open or shorted condition detected in the overdrive solenoid control circuit or Trans Relay Circuit in JTEC RE transmissions. Was MIL code 45. P0753 (M) Trans 3-4 Shift Sol/Trans Relay Circuits An open or shorted condition detected in the transmission 2-4 shift solenoid circuit (4-speed auto. trans. only).P0136 (M) 1/2 O2 Sensor Heater Circuit Malfunction Oxygen sensor heater element malfunction.

Aside from getting into an accident and having your wiring harness severely damaged, the other likely suspect is your PCM. These codes are not related to each other and indicate a much larger problem.

You're making the most common DIY mistake in thinking that whatever part is listed in the trouble code is what you need to replace. In your case the most important codes are:
P0135 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
P0141 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)

Oxygen sensors don't work well unless they're up to a certain temp. That's why they have heaters. So these codes are telling you there's a problem with the O2 sensor HEATER circuit. That could be a blown fuse or a problem with the wiring harness. Since the heaters aren't working, it makes perfect sense that you'd get the two other codes. Check the fuse for the O2 sensor heaters. Oxygen fuse in underhood fuse box (20A). If it's blown, replace it. If it blows again, you've got a short somewhere. Start by unhooking the all the O2 sensors. If the fuse doesn't blow, plug them in one at a time. Get it?

brake switch needs replacement.

try asking here

www.ukbookshelf.co.uk

this is fairly common with these o2 sensors. replace the one that has failed. they have a 4 wire set up that incorporates a circuit for a preheater that warms up so it reads more efficiently and even controlls emissions at start up. there is a fuse under the hood on the left side for o2 sensor heater circuit. check this first and then replace if necessary.

there is a fuse for the o2 heaters if one of the sensors blew the fuse they will all be out