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1997 w210 wagon E320 Avantgarde; 1986 BMW e28 528e; 1992 VW Golf Cabriolet; 1985 Isuzu Trooper II
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Discussion Starter #1
Hi guys,
My cruise control doesnt function. One of the causes would be the brake light switch, Ive read around. Is it accurate to say that if my brake lights go “on” each time i step on the brakes, then it means that i can conclude the cruise control fault is elsewhere and not the brake light switch ???
Cheers
Les
 

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1998 E320 base sedan @ 160kmiles
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Not necessarily. The brake light switch has two sets of contacts. The first is for the brake lights, and both the first and the second contacts are for the Traction Circuit.

If the brake lights work when you press the brake pedal while the car is running, but there are NO other warnings (like BAS/ Traction / ASR / ABS), I would look somewhere else. If you have these warnings at some point when you press the brake pedal, I would start with the brake light switch (bad contacts, out of adjustment, wiring, etc.).

If cruise control does not work with no other warnings / codes, I would check the the cruise control switch function and / or wiring.
 

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E250 Bluetec Sprinter250 Bluetec
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If I remember it right - the 3rd brake light is connected to 2nd circuit on pedal switch.
Meaning when all 3 brake lights work fine- the switch is good.
 

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1998 E320 base sedan @ 160kmiles
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If I remember it right - the 3rd brake light is connected to 2nd circuit on pedal switch.
Meaning when all 3 brake lights work fine- the switch is good.
Where did you get that information from?

Both tail brake lights and the center brake light are activated from the ICM (Illumination Control Module), and the ICM only monitors the first contact of the brake light switch (normally open). The only difference is that the tail brake lights are supervised, but the center light is not, which means that a burnt lamp in the center light will not cause a lamp defective warning.
 

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E250 Bluetec Sprinter250 Bluetec
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I was playing with the switch when I discover it.
It was years ago, so the memory of it is not crisp anymore.
 

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1998 E320 base sedan @ 160kmiles
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The brake stop switch second contact is normally closed. When one presses the brake pedal the first contact closes (brake lights) and second contact opens (BAS function). The Traction system measures the time it takes for the plunger travel that causes changeovers, and evaluates the emergency stop condition to activate BAS.

There are later models (2000 +) that require one additional contact for other purposes (goes to shifter module to disable shifter Park lock when closed), but if the brake stop switch has two contacts (4 pins), this is how it works.
 

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1997 w210 wagon E320 Avantgarde; 1986 BMW e28 528e; 1992 VW Golf Cabriolet; 1985 Isuzu Trooper II
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100 Posts
Discussion Starter #7
Thank you gentlemen ! Well, each time i step on the brakes, all brake lights (both left and right tail, plus the 3rd brake light) turn on too. Also, there are no other warning lights coming on on my dash.
So does that mean i move on to the circuitry and scratch the switch as suspect ??
 

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1998 E320 base sedan @ 160kmiles
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7,772 Posts
I would start with checking the cruise control switch functions, like does "the turn on" switch work? In some cases the cruise control switch assembly failures generate a fault code, but I am not sure if it generates a Check Engine Light. It probably will not, as it does not affect the engine function. I would check the codes from the ECU with a good scanner to see if P0565 code exists. If so, it will point to the CC switch assembly.

You could also check it electrically at the ECU connector D, pins 20 to 24 as indicated in the attached link.


With a proper scanner, you should be able to see what the ECU reads when you activate / deactivate CC functions.

There may be other reasons why the ECU decides not to activate the CC even if the switch is functioning fine. For that, you need live data from the ECU and other modules.
 

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1997 w210 wagon E320 Avantgarde; 1986 BMW e28 528e; 1992 VW Golf Cabriolet; 1985 Isuzu Trooper II
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100 Posts
Discussion Starter #9
I would start with checking the cruise control switch functions, like does "the turn on" switch work? In some cases the cruise control switch assembly failures generate a fault code, but I am not sure if it generates a Check Engine Light. It probably will not, as it does not affect the engine function. I would check the codes from the ECU with a good scanner to see if P0565 code exists. If so, it will point to the CC switch assembly.

You could also check it electrically at the ECU connector D, pins 20 to 24 as indicated in the attached link.


With a proper scanner, you should be able to see what the ECU reads when you activate / deactivate CC functions.

There may be other reasons why the ECU decides not to activate the CC even if the switch is functioning fine. For that, you need live data from the ECU and other modules.
Thank you very much mrboca
 
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