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Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3740
Experience:  15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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The wipers front and rear stopped working. Computer says

Customer Question

The wipers front and rear stopped working. Computer says short to ground on relay.
JA: Have you checked the fuses? Do you know if there is power to the wiper motor?
Customer: Yes all are good no power on fuse 100 for wipers.
JA: Tell me a bit more about what's going on so he can help you best.
Customer: Motors are good checked everything. Replaced switch only sprayers work.
JA: Are you hoping to fix this yourself?
Customer: Yes
JA: Great! What have you tried so far?
Customer: New relays new switch
JA: Is there anything else important you think the Mercedes Mechanic should know about your Mercedes?
Customer: Scanner says short to ground on run relay checked all wires going to fuse box
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Mercedes Mechanic about your situation and then connect you two.
Submitted: 6 months ago.
Category: Mercedes
Expert:  Lou P. master tech replied 6 months ago.

Hello, what year and model do you have?

Customer: replied 6 months ago.
2008 gl450
Expert:  Lou P. master tech replied 6 months ago.

OK, the most common issue is a poor connection at the rear fuse box or a bad relay, i see what you have checked and tested so far, let me get a wiring diagram up and see what we can check. give me a few min

Customer: replied 6 months ago.
Ok thank you
Expert:  Lou P. master tech replied 6 months ago.

no problem at all

Expert:  Lou P. master tech replied 6 months ago.

I am still here, its a pain to find lol, the system uses a lot of communication wires.

Expert:  Lou P. master tech replied 6 months ago.

ok so relays A and B in the front relay /fuse box in right front of engine are for the wipers, swap the two with each other see if the front wipers work, keep in mind the wipers will NOT wipe if the hood or doors are open, so you need to open the hood and manually push down the hood latches so the module thinks the hood is closed.

Expert:  Lou P. master tech replied 6 months ago.

WE will focus on the front wipers first

Customer: replied 6 months ago.
Did that nothing
Expert:  Lou P. master tech replied 6 months ago.

ok, test fuse 100 when someone is activating the wipers to see if power is flowing through it

Customer: replied 6 months ago.
No power threw it.
Expert:  Lou P. master tech replied 6 months ago.

ok, next , remove relay B

test across the fuse box where terminals of 85 and 86 would attach and see if the test light comes on when activating the wipers.

Expert:  Lou P. master tech replied 6 months ago.

terminals 85 and 86 of the relay are the activation terminals that will allow 30 supply power to 87 when activated

Customer: replied 6 months ago.
85 power 86 ground
Expert:  Lou P. master tech replied 6 months ago.

OK so far so good,

next see if 87 has power

Expert:  Lou P. master tech replied 6 months ago.

NOT 87a

Customer: replied 6 months ago.
Power on 87
Expert:  Lou P. master tech replied 6 months ago.

if 87 has power then jump 87 to 30 and the wiper motor should turn on and fuse 100 should get power.

Expert:  Lou P. master tech replied 6 months ago.

there have been multiple issues with the front fuse box melting internally so lets keep that in mind

Customer: replied 6 months ago.
Scanner says component f58k on off relay has short to ground f58k defective or missing
Expert:  Lou P. master tech replied 6 months ago.

lets not worry about the scanner just yet, have you jumped power ?

Expert:  Lou P. master tech replied 6 months ago.

also there must be another letter after the K, K means relay, so the next letter should be the relay position. so F58 (fuse box) K (relay) then the letter position

Customer: replied 6 months ago.
if you take relay a out and jump it they work with relay a in pops power probe
Customer: replied 6 months ago.
F58kb
Expert:  Lou P. master tech replied 6 months ago.

OK that is the relay we are working on, that is why most likely

Expert:  Lou P. master tech replied 6 months ago.

wait, the wipers work with relay A removed????

Expert:  Lou P. master tech replied 6 months ago.

ok let me rephrase, you are jumping the wipers at what relay.?

Customer: replied 6 months ago.
No if I jump power with it in it pops fuse on power probe.
Expert:  Lou P. master tech replied 6 months ago.

ok , here is the diagram i am looking at,

Expert:  Lou P. master tech replied 6 months ago.

with relay B installed and relay A removed see if power and ground are present when switch activated across 85-86

Customer: replied 6 months ago.
85 dead 86 power 85 nothing
Expert:  Lou P. master tech replied 6 months ago.

ok , 85 comes from front sam, so next i ask that you access the front sam and check for corrosion in the connections, also does you scanner have the capability to activate the wiper circuit?

Customer: replied 6 months ago.
but it doesn't come on with it either.
Customer: replied 6 months ago.
What is front sam
Expert:  Lou P. master tech replied 6 months ago.

front sam is the control module next to the battery under the passenger front seat

Expert:  Lou P. master tech replied 6 months ago.

its the control module that controls the front end electronics

Customer: replied 6 months ago.
Nothing looks wrong
Expert:  Lou P. master tech replied 6 months ago.

you see the black module with like 8 connections on top? right next to the battery

Expert:  Lou P. master tech replied 6 months ago.

if you are activating the wipers and nothing is happening and continuity is good with the sam then the sam is faulty.

Customer: replied 6 months ago.
Would this power cigarette lighter also it's dead too
Expert:  Lou P. master tech replied 6 months ago.

Which one? some models have more than one

Customer: replied 6 months ago.
Front in consel
Expert:  Lou P. master tech replied 6 months ago.

ok checking

Expert:  Lou P. master tech replied 6 months ago.

no that is fuse 46 in rear fuse box on right side of trunk

Expert:  Lou P. master tech replied 6 months ago.

connector C pin 10 is the wire for the relay A activation on the front sam, connector C is a big 40 pin connector, there are 2 that are the same, the wire color you are looking for is pink with black stripe.

Expert:  Lou P. master tech replied 6 months ago.

if you came to my shop, the first thing i do is try to activate with the scan tool, if the scan tool shows that the wiper switch is in fact seeing a signal that it is activated and the front sam is not sending out a signal, that tells me the wire is open from the sam to the fuse box or the sam is faulty, as for the rear we would need to check the functions at the rear fuse box. let me know when you are ready to attack that one.

Expert:  Lou P. master tech replied 6 months ago.

also with the key on, see if there are other functions that do not work, we had issues with the circuit 15 relay in the rear fuse box, the quickest way to tell was to check all the fuses for power and let me know what fuses do not have power , that will tell me if we have a dead circuit.

Customer: replied 6 months ago.
I'm checking for power on pink and black right
Expert:  Lou P. master tech replied 6 months ago.

no, you are checking for a ground signal when wipers are activated. let me 100% verify

Expert:  Lou P. master tech replied 6 months ago.

yes its a ground signal when wipers are activated. so you will have to do this, insert all the relays, erase the codes. then backprobe the wire and see if you get a ground when activating.

Customer: replied 6 months ago.
It's hot pink and black
Expert:  Lou P. master tech replied 6 months ago.

Ok if its hot that is just the hot side backfeeding through the relay, if you remove the relay A it will ,most likely kill the power on the wire. so far as long as we are on the same page, the front sam is bad.

Customer: replied 6 months ago.
With relays out 9.6 on pink and black
Customer: replied 6 months ago.
What about front fuse box
Expert:  Lou P. master tech replied 6 months ago.

9.6 volts? if so , positive or negative?

Customer: replied 6 months ago.
Hot
Expert:  Lou P. master tech replied 6 months ago.

the module may send out a small voltage to check to see if the circuit is connected and thats where it knows when to throw an open circuit fault code.

Expert:  Lou P. master tech replied 6 months ago.

ok disconnect the connector at the sam and see if the wire still has power.

Customer: replied 6 months ago.
I'm going to change both front fuse box and sam
Expert:  Lou P. master tech replied 6 months ago.

ok the front sam will need coded if replaced with new, you can get lucky and not need coding if you get a used one from same year with same options.

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