[one-O-one Racing]

Hi,

I have a Maserati Trofeo racecar in GT4 Spec. I've been experiencing a strange issue with the gearbox warning light during my last outing at Spa-Francorchamps. I've conducted extensive diagnostics, and here's what I've found:

This is a factory racecar, not a converted streetcar, so while some parts are standard, others are unique to the racecar.

I used the diagnostics tool that came with the car, and it reads the "brake switch error code", as described several times on this forum. But this car has not the ususal brakeswitch but a very basic pressure activate NO switc, connected directly to the brake pressure line. example below:

Key details about the car's braking system:

• No ABS or ESP
• No power-assisted brakes
• Factory-fitted Alcon pedalbox

During track sessions, the gearbox warning light comes and goes, but the car and gearbox work normally without any issues.

Here are my findings from further testing at home:

• The warning light comes on EXACTLY 10 seconds after releasing the brake pedal.
• The warning light stays on.
• When the brake pedal is pushed, the light goes out after approximately 0.5 seconds.
• Release the pedal, and 10 seconds later, the light comes on again and stays on.

Additional observation: When I disconnect BOTH rear light clusters, the error is gone and doesn't come back. Disconnect only one, and the error remains, regardless of which one is disconnected. Taillights are original like the streetcar, but only the outer ones are used. The inner ones are disconnected and only there for esthetics.

The most intriguing thing here is the exact 10 seconds it takes every time before the error starts after releasing the pedal. So, I think there must be some kind of checking procedure the TCU is doing that takes exactly 10 seconds.

Can anybody provide insight into what could be the reason? What is measured or checked by the TCU? What takes 10 seconds?

 

[Cheburator]

I would actually change the switch - it's cheap and without ABS, bleeding the brakes on the GT4 is easy...

 

[Catmanv2]

I would actually change the switch - it's cheap and without ABS, bleeding the brakes on the GT4 is easy...

That would be my start as well

C

 

[one-O-one Racing]

Hi,
Thanks for your input.
I've replaced this switch by another normal switch and results were the same. This very basic switch just connects the two connection toghether, or disconects it. It doesn't connect to anything else. No internar resistor, No grounding of the wires. No nothing. IThis type of switch was used in the '60's and '70's in Mini Coopers and early motorcycles. It' even doesn't have a Maserati partnumber.

Her's a picture of the switch in my car, highligted in red:

I also tested to disconect the two wires, what In my opninion does exactly what a Normal Open contact does, and results are identical. Shorting the two wires is like pressing the pedal. Disconecting it is like releasing the brake.

I'm pretty sure it isn't the switch.

Any other ideas?

 

[MaseratiByChance]

• The warning light comes on EXACTLY 10 seconds after releasing the brake pedal.
• The warning light stays on.
• When the brake pedal is pushed, the light goes out after approximately 0.5 seconds.
• Release the pedal, and 10 seconds later, the light comes on again and stays on.

Additional observation: When I disconnect BOTH rear light clusters, the error is gone and doesn't come back. Disconnect only one, and the error remains, regardless of which one is disconnected. Taillights are original like the streetcar, but only the outer ones are used. The inner ones are disconnected and only there for esthetics.

The most intriguing thing here is the exact 10 seconds it takes every time before the error starts after releasing the pedal. So, I think there must be some kind of checking procedure the TCU is doing that takes exactly 10 seconds.

Can anybody provide insight into what could be the reason? What is measured or checked by the TCU? What takes 10 seconds?

This may sound lame but try replacing all your tail/brake lamp bulbs with the OEM parts. Could be the bulb resistance is higher or lower on one of them causing the fault.

 

[Rennz]

Is there not another switch located on the upper portion of the pedal assembly on the interior?

 

[sammyf]

@one-O-one Racing When you connect the diagnostic scanner to the TCU unit, you should be able to monitor "Brake Switch" status. I assumed you tried to Press/Depress the brake pedal a few times and is the status reading correctly?

 

[Catmanv2]

Is there not another switch located on the upper portion of the pedal assembly on the interior?

Yeah, have to say that's a new concept on me.

@one-O-one Racing if you short the switch wires manually, does it also trigger the fault?

C

 

[one-O-one Racing]

@one-O-one Racing When you connect the diagnostic scanner to the TCU unit, you should be able to monitor "Brake Switch" status. I assumed you tried to Press/Depress the brake pedal a few times and is the status reading correctly?

The status reads correctly. Nothing unusual.

 

[one-O-one Racing]

Yeah, have to say that's a new concept on me.

@one-O-one Racing if you short the switch wires manually, does it also trigger the fault?

C

If I short the wires it’s like the pedal is pressed. So this clears the error. When I “un-short” the wires, error comes after exac10 seconds.

 

[one-O-one Racing]

This may sound lame but try replacing all your tail/brake lamp bulbs with the OEM parts. Could be the bulb resistance is higher or lower on one of them causing the fault.

The car uses the standard light clusters with the leds. So no bulbs to replace.
I measured the current through the switch in several situations.

• 970 mA when both taillights are connected.
• 520 mA when left light is disconnected. So that’s the right taillight + TCU
• 450 mA when right light is disconnected. So that’s te left twilight +TCU
• 1mA when both are disconnected. So that’s only the TCU

 

[one-O-one Racing]

Is there not another switch located on the upper portion of the pedal assembly on the interior?

There’s no other switch.
There are two pressure sensors on the front and rear brake line, connected to the can line to display the brake pressure of the front and rear wheels, so you can adjust the brake balance. These are also used for data logging and video overlay.
This system does not communicate with the tcu and is a stand alone system.

 

[one-O-one Racing]

Thanks for all the input.

But I think I’ve solved the issue!!

I was thinking it could be some kind of noise on the wires, when the wires aren’t connected. The tcu sees this noise and triggers the error.

so I put a 2K Ohm resitor parallel with the switch. This way there is a minuscule current of 6 mA constantly flowing, getting rid of the noise.
While braking the resistor is shorted and thus eliminated.

this current is to low to light the brake light or to be seen by the tcu.

I’ve tested it in real life and everything seems to work now as it should.🥳🤩🥳.


What do you all think? Is this a good solution? Should i implement this resistor permanently?

 

[MaseratiByChance]

The car uses the standard light clusters with the leds. So no bulbs to replace.
I measured the current through the switch in several situations.

• 970 mA when both taillights are connected.
• 520 mA when left light is disconnected. So that’s the right taillight + TCU
• 450 mA when right light is disconnected. So that’s te left twilight +TCU
• 1mA when both are disconnected. So that’s only the TCU

Is there another similar vehicle that you could use to measure the current or do a swap? Is there a number you could call to speak with a tech/engineer to ask about the resistance/current through the lamps?

Thinking outside the box, measure the resistance of each lamp and replace the lamps with a resistor of each value to see if that fixes the problem. Should not be to difficult. Determine the brake circuit and ground and insert a modified resistor attached to a similar terminal. For example, put a 26 ohm resistor across both lamps (lamps disconnected), the try putting a 23 ohm resistor across the lamps.

I think the current/resistance should be equal but don't know for sure. In every day vehicles when a bulb burns out or has a higher resistance that will turn on a warning lamp.

 

[Rennz]

There’s no other switch.
There are two pressure sensors on the front and rear brake line, connected to the can line to display the brake pressure of the front and rear wheels, so you can adjust the brake balance. These are also used for data logging and video overlay.
This system does not communicate with the tcu and is a stand alone system.

This was the switch I was referring to.
COMPLETE PEDAL BOARD UNIT parts for Maserati GranCabrio (2013-2015) MC | Scuderia Car Parts

Part #

7

958694

PUSH-BUTTON SWITCH

 

[MaseratiByChance]

Thanks for all the input.

But I think I’ve solved the issue!!

I was thinking it could be some kind of noise on the wires, when the wires aren’t connected. The tcu sees this noise and triggers the error.

so I put a 2K Ohm resitor parallel with the switch. This way there is a minuscule current of 6 mA constantly flowing, getting rid of the noise.
While braking the resistor is shorted and thus eliminated.

this current is to low to light the brake light or to be seen by the tcu.

I’ve tested it in real life and everything seems to work now as it should.🥳🤩🥳.


What do you all think? Is this a good solution? Should i implement this resistor permanently?

I still of the mind it has something to do with the resistance of the brake lamps. One or the other may have too high or low value. They should be of equal value. But glad you stopped the warning lamp from coming on.

 

[one-O-one Racing]

This was the switch I was referring to.
COMPLETE PEDAL BOARD UNIT parts for Maserati GranCabrio (2013-2015) MC | Scuderia Car Parts

Part #

7

958694

PUSH-BUTTON SWITCH

The part and diagram you're refereing to is from he streetversion. As mentioned this car has from the factory a completky different pedalbox. Non brake assisted. So this witch is not compatible. That's why it's a pressure operated switch, an not the normal push switch. Thanks anyway.

 

[Rennz]

The part and diagram you're refereing to is from he streetversion. As mentioned this car has from the factory a completky different pedalbox. Non brake assisted. So this witch is not compatible. That's why it's a pressure operated switch, an not the normal push switch. Thanks anyway.

Yes, I understand. And you found a solution. The reason I brought it up is because on many cars there are switches on both the brake master cylinder and the pedal box. The fluid pressure switch on the master cylinder normally is for the red brake warning light on the dash and the switch on the pedal box is for the rear brake lights.

 

[Church of Noise]

I still of the mind it has something to do with the resistance of the brake lamps. One or the other may have too high or low value. They should be of equal value. But glad you stopped the warning lamp from coming on.

That would be my assumption too. Maybe replace the rear light with the lower resistance (and the extra resistor) and see what happens?
Greetings from another Belgian

 

[one-O-one Racing]

Yes, I understand. And you found a solution. The reason I brought it up is because on many cars there are switches on both the brake master cylinder and the pedal box. The fluid pressure switch on the master cylinder normally is for the red brake warning light on the dash and the switch on the pedal box is for the rear brake lights.

Ah. I see.

But i think it's the signal of the switch you're refering to, is the one that's now taken over by my pressure switch.

Is there a pressure operated switch in the streetversion? I don't seem to find it in the documentation i find online. I would think its only the mechanical switch.