No speedo abs on

[Goodtin]

I have a 1998 express 1500 the speedo doubles abs light is on no codes . I think it a ground problem where do I start? I have a stock 4 vol manual , it’s like reading a foreign language.

[MountainManJoe]

Welcome to the forum.
Sounds like you have a speed sensor problem. But you need to isolate which one it is. A diagnostic scan to read the codes that are triggering the ABS light should provide clues. Just swing by an Autozone, Advance, O'reily etc. or whatever you have. They all give courtesy scans.

[Goodtin]

Already changed vss no other codes . My scanner won’t comm with abs but my friends snap on did no codes all looks correct till you drive it then the speedometer doubles and abs light comes on .it also stacked shifts in to overdrive at 30 mph.

[MountainManJoe]

OK so I'm not typing for nothing, is there any other troubleshooting you did that you did not mention?

Already changed vss no other codes

Well, when you just guess without checking, you end up wasting a lot of time and money without actually fixing anything.

From the ABS operation description in the service manual (which it sounds like you have),(page1 , page2), the brake control module monitors three speeds.

Looking at the ABS electrical schematics (attached below), the brake module uses left and right front wheel speed sensors, and a vehicle speed which it gets from the main VCM. It's very common for WSS to fail from something called rust jacking.

My scanner won’t comm with abs but my friends snap on did no codes

If the warning light is on, then there are stored codes or the brake module isn't responding. You can't just use any old scanner. the tool has to have ABS capability so try a different one, and make sure the EBCM actually responds (otherwise it could have a loose or corroded connector)


Are you using factory size tires that are inflated properly?

[Goodtin]

My scanner doesn’t comm but a snap on did no codes my scanner did see abs when I got the van but not now . At the moment I am cleaning all the grounds and take a look at connections I did 5 grounds and have gained 1 volt on the gauge someone installed in side. I have the drivers side frame rail to do next . I don’t see any flat straps they talk about and have a small ground wire that look joined to a larger wire a #10 or 8 to a #14or 16 on the pass side head rear. Joined like speaker wires are paired. is this normal or have I found the problem? There are a lot of grounds under there.

[MountainManJoe]

from the above diagram, you can see the brake module is grounded through G101 and G102

First though, I would just try unplugging the brake module and plugging it back in a few times. (always disconnect the negative battery cable before working on electrical components).

I don’t see any flat strap

Your engine to ground cable is here and here but if that was bad then the van probably wouldn't go anywhere, or would run rough.

have gained 1 volt on the gauge

What is the system voltage? (engine on and off?)




Description of Ground Locations from service manual:

Code: Select all

COMPONENT		LOCATION
G100			LH engine compartment, near fender well
G101			Engine harness, near thermostat housing
G102			Engine harness, near generator bracket
G103 (4.3L)		Engine harness, at generator bracket
G103 (5.0L, 5.7L, 7.4L)	LH front of Engine harness, near A/C compressor
G104			RH frame rail near front of engine
G105			RH lower front of engine
G106			LH engine compartment, at bulkhead
G108			LH engine compartment, near fender well
G109			RH engine compartment, near fender well
G110			RH engine compartment, near negative battery post
G112			LH engine compartment, under brake master cylinder
G200			Behind LH kick panel near power door lock control module
G201			IP harness behind LH kick panel near IP fuse block
G202			P harness behind LH kick panel near IP fuse block
G300			LH frame rail near auxiliary battery
G400			LH rear corner of interior cabin, behind rear wheel house
G401			RH rear corner of interior cabin, behind rear wheel house
G402			RH rear corner of interior cabin, behind rear wheel house

Attached: GM Technical Bulletin 09-06-03-004 which describes how connector fretting corrosion can cause failures of various modules, how to remedy and prevent it:

Buick TSB 09-06-03-004E.pdf

(206.62 KiB) Downloaded 50 times

Location of EBCM (LH frame rail near center of vehicle Engine):

ebcm.png (26.74 KiB) Viewed 685 times

[Goodtin]

12.1 off never been more than 13.2 running now 14.2 running . And I’m still cleaning grounds . There are no flat braided grounds? Always see them all green and week on most gm products. None on rad support ?

[Goodtin]

Does the fact it’s an American van conversion change some of the wires . I’m not finding all of the grounds . They have a different hvac unit ft and rear.

[Goodtin]

I have tryed everything I can find speedometer is now double abs light now new alternator 3 new battery ends and darters cables . I’m stuck .

[Goodtin]

Can tire size do all this? The new tires are a little taller one in a half inch taller

[MountainManJoe]

Of course tire size affects speedo/odo/abs/etc.
But it wouldn't double it.

https://tiresize.com/calculator/

[Goodtin]

Does anyone understand this 3 wheel abs?

[MountainManJoe]

Read your speed with an OBD scan tool. If it’s good then you probably have a faulty cluster. As for the abs light, have you checked those WSS? Like I said it’s common for them to fail