Help need diagnosing a brake problem

[MrBrady]

2014 Genesis R-Spec 115,000 miles
For the past two years I've had an intermittent issue where the brake pedal will almost go to the floor while braking, but pumping the brakes once or twice firms it up. It use to happen maybe once very couple months, but recently happens daily.

In December 2023, I changed the rotors and pads, and flushed the brake fluid (first time in 100,000 miles). The issue remained.

A couple weeks ago I had a mechanic change the master cylinder. The system was bled through the ABS/HECU only (not at the wheels). The problem totally went away and the brakes were great for 15-20 miles, then they locked up (heavy, heavy brake binding). ESC and autohold warning lights came on.

Towed to a brake shop. They said it needed to be flushed. So they did, but had a really hard time doing it, saying the HECU was bad, throwing code C1237 Primary pressure sensor signal.

Ordered a rebuilt HECU from eBay from iam-motors. Installed it today and flushed the system following the HECU recall TSB from Hyundai - bleed at wheels RR, LF, LR, RF, then the ABS/HECU module, then calibrate a few items.

Car drove fine for about 5 miles, then started to binding again with another ESC light. Code C1237 Primary pressure sensor signal comes back again, as does C1354 Pressure sensor (Wh1) - Other, C1356 Pressor sensor (Wh2) - Other. Feels like it's the back brakes, but I'm not completely sure.

Brake pedal feels more firm than normal and is very sensitive. A slight touch of the pedal applies the brakes enough to stop. So lightly that it doesn't even trigger the brake lights to come on.

I can do a HECU air bleed through a scan tool and it relieves the brake dragging about 50% - enough to drive around the block before the brakes start seriously binding again.

Any suggestions of what to check for next?

 

[Gunkk]

Been following your dilemma. Sounds like it is uncertain where the problem (binding) exactly is.

Most of the time, binding in a single wheel is failure of one or more components of a caliper assembly or the parking brakes: piston, pin, or pads/shoes. Easy enough to identify the offending wheel with a contactless thermometer.

If it's an issue that affects multiple wheels at the same time then I'd suspect a hydraulic issue with the HECU, master cylinder, pedal adjustment, EPB issue, or plumbing.

In the troubleshooting section of my manual it lists "brake pedal free play" as the #1 most likely cause of brake drag, which I find interesting given that you state that the pedal feels abnormally sensitive. The manual states that free play must be adjusted when the master cylinder is changed.

So perhaps it's as simple as the pedal free play needing adjustment?

 

[joegr]

...A couple weeks ago I had a mechanic change the master cylinder. ..., then they locked up (heavy, heavy brake binding). ESC and autohold warning lights came on.
... Code C1237 Primary pressure sensor signal comes back again, as does C1354 Pressure sensor (Wh1) - Other, C1356 Pressor sensor (Wh2) - Other. ... A slight touch of the pedal applies the brakes enough to stop. So lightly that it doesn't even trigger the brake lights to come on.
...

Any suggestions of what to check for next?

Sounds like the mechanic did not correctly adjust the push rod between the brake booster and the new master cylinder. At least that's where the adjustment usually is.

 

[MrBrady]

Sounds like the mechanic did not correctly adjust the push rod between the brake booster and the new master cylinder. At least that's where the adjustment usually is.

Thank you. That's a great suggestion. I do not believe any adjustment was done during installation.

 

[MrBrady]

Been following your dilemma. Sounds like it is uncertain where the problem (binding) exactly is.

Most of the time, binding in a single wheel is failure of one or more components of a caliper assembly or the parking brakes: piston, pin, or pads/shoes. Easy enough to identify the offending wheel with a contactless thermometer.

If it's an issue that affects multiple wheels at the same time then I'd suspect a hydraulic issue with the HECU, master cylinder, pedal adjustment, EPB issue, or plumbing.

In the troubleshooting section of my manual it lists "brake pedal free play" as the #1 most likely cause of brake drag, which I find interesting given that you state that the pedal feels abnormally sensitive. The manual states that free play must be adjusted when the master cylinder is changed.

So perhaps it's as simple as the pedal free play needing adjustment?


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Is free play a physical adjustment somewhere or through the computer?

 

[Gunkk]

Physical.

 

[MrBrady]

So perhaps it's as simple as the pedal free play needing adjustment?


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Where can I find these troubleshooting documents? Looks super useful!

 

[joegr]

Where can I find these troubleshooting documents? Looks super useful!

One source: Hyundai Genesis - Google Drive

 

[MrBrady]

UPDATE: Took it to PepBoys today to have them diagnose. They are fairly sure it's related to the master brake cylinder. Their tech got stuck on the road for an hour, but figured out if the lines to the master brake cylinder are cracked open, the brake binding is released.

Their tech said that it should be an OEM part because Hyundais are very sensitive and a aftermarket part brake line connectors may not line up perfectly, causing incorrect pressure.

The mechanic bought and installed the part a couple weeks back when the binding issue started happening. Noted it is a new OEM (not remanufactured).

Still going to look at free pedal position. If that doesn't solve it, will remove and reinstall the master brake cylinder and check the booster piston while it's off.

 

[MrBrady]

Reading through the GDrive Repair Files (SUPER helpful!), but am not clear on the bleed procedure. Should the engine be running or ignition only?

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[Gunkk]

Pretty sure you'll need IGN_ON for the HECU bleed, but my manual doesn't say either way. Once the HECU is done you should be able to bleed the rest of the system (lines and calipers) with IGN_OFF.