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Doug C.
Doug C., ASE Certified Technician
Category: Car
Satisfied Customers: 6194
Experience:  16 years automotive and OTR repair including specialized training from Toyota and Mitsubishi
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Mitsibishi Colt: Hi I drive a mitsibishi colt 2008 model with

Resolved Question:

Hi I drive a mitsibishi colt 2008 model with only low 40000 km on the clock. it is in good condition and drives well. But when i am at work driving out of the car parking area which is about 6 levels high, when approaching the corner to go down to the next level, i break and sometimes the breaks lock and the car swerves and i can hear a loud knocking noise. at that time i try release the breaks and even try pumping them but i have no control over it. i have had to use the handbrake to stop. this only last a few seconds but then when i drive off from the corner onto the straight stretch the car splutters a bit and sometimes swerves a bit. very scarey as i have no control for those seconds. this only happens infrequently. have also driven the same car park with another car with no problems.i have had the car looked at by my local mechanic and he cant find anything wrong and says the breaks are perfect. please help... Thanks
Submitted: 1 year ago.
Category: Car
Expert:  Doug C. replied 1 year ago.
Hi,

When this problem occurs, do the brakes remain engaged or do they stop braking in addition to being unresponsive?
Customer: replied 1 year ago.

hi


its hard to determine 100% because im only going down the ramp very slowly about 10kmh due to be scared about this happening. but when i break the car still jerks forwards and swerves to the ides before stopping so it eventually stops but not right on breaking and not for a few seconds. infact ive had to use my handbrake a couple times to stop completely. .

Expert:  Doug C. replied 1 year ago.
Thanks.

Do you have ABS on this vehicle? ASC/TCL?
Customer: replied 1 year ago.

yes i have ABS breaks

Expert:  Doug C. replied 1 year ago.
Thanks.

Are you getting any feedback inside the car (apart from the knock sound)? For example either a beep or a light coming on momentarily?
Customer: replied 1 year ago.

no nothing

Expert:  Doug C. replied 1 year ago.
Hmm.

This happens pretty consistently on this ramp... if you approach it "normal" it will pretty much always behave this way?
Have you ever had the condition occur anywhere else, and if so was it on an incline as well?
Customer: replied 1 year ago.

no it only seems to happen when coming down a ramp like that on the decline and i have approached it at a normal speed until this started happening but after its happened and i drive off from the ramp on the flat straight road it swerves and jerks a bit and this all happens probably only every 10th time i go down it.

Expert:  Doug C. replied 1 year ago.
Thanks.

Does the clunk sound seem to come from under the hood by the ABS pump? How many sounds do you normally hear when it occurs (how long does the knocking occur for, etc)?
Customer: replied 1 year ago.

the knocking sounds like its coming from under the car and it lasts about 3 seconds

Expert:  Doug C. replied 1 year ago.
Thanks.

Is the knock rhythmic to itself or to wheel speed (it's okay if you are unsure)? When the knocking is occurring, is the response from the brakes notably different than after the knocking stops?
Customer: replied 1 year ago.

i think once the knocking stops the breaks seem to come right

Expert:  Doug C. replied 1 year ago.
Thanks.

If you had to pick a side that the knocking noise was coming from, would you say it is more passenger side under the front of the car?
Customer: replied 1 year ago.

under the front of the car i think

Expert:  Doug C. replied 1 year ago.
Thanks.

At this point I think we can pretty safely determine that the ABS is malfunctioning.
When the ABS takes over, the brake pedal will have limited to no effect on braking as the hydraulic system is re-routed under ABS control. The ABS modulator pump makes a knocking sound when the solenoids activate. The pump is located underneath the front of the car (about half way down the firewall).

Of course the important question is why is it doing this of course.
It seems like the incline is a pretty good catalyst for this. Have you noticed a similar propensity on other inclines?
Customer: replied 1 year ago.

thanks. no i have only noticed it when going down not up. im off to work again now so may be a bit delayed in responding. Thank-you

Expert:  Doug C. replied 1 year ago.
I'm sorry I was using incline for either direction.... just because I don't like the sound of declines to differentiate.

At this point I would see if you can get the vehicle in to have the ABS system scanned for faults. If nothing shows then it would be best if it could be driven in a manner to create the issue while it is being monitored on the scan tool to see what is occurring before/during the malfunction.

Based on the information you have provided, my first suspicion would be that there is a problem with the G sensor (located in the bottom of the center console). The G sensor determines not just G forces but also tipping.... meaning going down a slope would cause a different reading to occur on this sensor which may be erroneous and cause the pump to activate thinking it is slipping.
Beyond that I would look into possible wiring issues where when the vehicle is not level the wiring may be moving just enough to cause an issue, followed by a potential internal fault in the pump.

Realistically.... I have changed out a fair number of these G sensors for reading out of range, that is much more probable.
Please try to get this in for service as soon as possible... this is a major safety hazard as you are well aware, and while it is momentary right now and not real consistent, it could become more consistent at any time or become no longer momentary putting you into a very dangerous position if you are at a speed beyond the abilities of your emergency brake.

If I can assist you further just let me know.
Doug C., ASE Certified Technician
Category: Car
Satisfied Customers: 6194
Experience: 16 years automotive and OTR repair including specialized training from Toyota and Mitsubishi
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