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Matt
Matt, Engineer
Category: Australia Car
Satisfied Customers: 21500
Experience:  Automotive Engineer for 20 years, BEng hons degree,
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The ABS service light and ASC service light comes on

Customer Question

Hi, the ABS service light and ASC service light comes on intermittently
JA: Is it just the ABS light? Or is the brake system warning light on, too?
Customer: Just the ABS light and it says that the ABS needs a service
JA: What is the model/year of your Mitsubishi?
Customer: 2010, vrx
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: I took it to the Mitsubishi dealer that I bought it from.. they checked everything and installed some new software but it hasn't fixed it. They are now saying that it needs a new ABS unit
JA: Anything else you want the mechanic to know before I connect you?
Customer: Just that occasionally, these warning lights go off and all that is left is the yellow engine light
Submitted: 7 months ago.
Category: Australia Car
Expert:  Matt replied 7 months ago.

Hello

If the ABS light is staying on then this would indicate a fault with the system which shouldn't effect the regular braking performance so the car is still safe to drive.

The quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious.

However with ABS systems 99% of the time its a problem with one of the wheel speed sensors and I'd first check the connections at all four corners first for any signs of corrosion or chafed wiring.

The sensor is located in the wheel hub so you'll have to remove each wheel in turn to inspect them all.

Also check that the toothed wheel that the sensor points to is clean and free of any debris.

you can check each sensor's function by plugging the two output wires into an AC voltmeter and spinning the wheel quite quickly, you should get a voltage signal that increases with rev's.

Its possible that the fault is only a bad connection to one of the wheel sensors.

This may be remedied by removing each wheel in turn and unplugging each sensor and cleaning the contacts with a squirt of electrical contact cleaner. Then refitting.

Customer: replied 7 months ago.
Thanks for your help, the Mitsubishi Dealer is trying to get me to pay for a whole new ABS unit before they do any other checks.
Expert:  Matt replied 7 months ago.

I'd ask for the fault code that they've pulled off, I'll then be able advise further

Customer: replied 7 months ago.
I used an OBD2 scanner on the car and it came up with P1773?
Expert:  Matt replied 7 months ago.

Hello

P1773 is indicating that a malfunction occurred in the ABS system that is outside the range of the enhanced OBD systems field of vision. - so sadly not a lot of help - however to go straight in a request a new ABS unit is the wrong way about it

its very likely a faulty ABS speed sensor. They are well known for failure on this model, particularly the right rear and the left front for no known reason. On extremely rare occasions the ABS pump unit can fail, but we are talking about 1/1000 cases.

At this point you are going to need to get the car to a shop that has a scan tool with full ABS/ASC support so that the fault codes can be identified and part replaced.

If you can not get to anyone that has a full scan tool (not just a code reader)

Then its back to checking wheel speed sensors as I've already mentioned

If you unplug each wheel speed sensor, you can probe the two wires of each connector (on the sensor end) with a meter set to AC voltage. In this state, if you spin the wheel at hand you will see voltage appear on the meter. Not much, but a little. In this respect you could check each sensor this way and if one shows 0 at all times with wheel spinning, then you know that sensor is bad.

Of course the ideal scenario would be to scan it with a proper scan tool, as there is still the slim chance something else apart from a speed sensor is amiss. As I said though, that is really the only common thing.

Maybe every once in a while we'll see the stop light switch malfunction (you wouldn't have any brake light control if this were the case)

The sensors are note terribly cheap on this model, averaging about $250-275 each. With four of them possible to go bad, plus the slight chance that there is something beyond that going on, it would be money well spent for a quick ABS/ASC scan to see what is going on.
Once the problem is corrected, the ABS capable scan tool will be required to clear the faults, and then the OBD faults (P1773) will need to be cleared as well.

Expert:  Matt replied 7 months ago.

Hi

do you still need help?

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