ABS

As I have been reading through the topics that deal with this wonderful system, If I'm wrong please let me know.

If the abs system the brain of it is not working I will have driveabilty issues I got a used computer from a j-yard and the light didn't come on so I was right at the beginning again I will be tearing the dash apart to double check the light But any would be great Thanks in advance to everyone that has helped so far

yo E,

89 Bronco, Correct?  if so;

Anti-Lock Brake (ABS) - RABS (RABS II 87-92)

Yes, a bad RABS moule or a system component will cause driveability issues; such as;

DTC 27, 29, 452, P0502, P0503, PO716, PO718; Insufficient input from VSS.; "...A more difficult problem to identify is a VSS that works, but sends out the wrong signal for a given vehicle speed. In some cases, a wrong reading from the VSS may still cause a code to be set. For example, if the VSS signal tells the computer the vehicle is traveling 60 miles an hour, but the throttle position sensor and MAP sensor tell the computer that the engine is idling, the computer will be confused. And a confused computer should set any of the following codes: Ford 27, 29, 452. On a vehicle that uses the VSS as a safety device, a defective sensor may send out a wrong "too fast" signal, shutting down fuel flow at the wrong time. Although this doesn’t happen often, it can be a difficult problem to identify. The customer will probably describe it as a random or intermittent sudden loss of power and poor performance, onlyto have the engine resume normal operation. Routine diagnostic checks of the engine in the shop won’t show any problem because there isn’t a problem with the engine or the ECM..." read more
Source: by wellsmfgcorp.com

So do this Test at home

RABS Self Test; except 93-96; "...The 90 service manual gives a routine to pull RABS codes. When the light comes on, don't turn the truck off before reading the codes. Put it in park, chock both front & rear of the wheels, note whether the red brake light is lit also, then momentarily ground the test connector. The test connector comes out of a large loom under the dash, coming through the firewall, near the parking brake. On mine there are 2 similar connectors in that area, the correct one has only 1 black wire with an orange tracer running to it, & was hidden on top of the loom. The correct one is hanging down on the bottom right of the pic below. After you've grounded & ungrounded the wire, the yellow abs light starts to flash. Count the flashes. It said to not count the 1st series, because it may start in the middle. The last flash of the series is a long flash. Then it repeats over & over, until you turn the key off. Count all of the short flashes & the long one together (So 4 short & 1 long is code #5). If I remember right, it should be a number between 2 & 15 or so. If you follow Steve83's sig link, & then go to his Brakes & Hubs album, he has the code definitions for RABS.." READ MUCH MORE; miesk5 Note, Steve83 wrote, The RABS module won't ***** up the speedo or trans the way the 4WABS module can, and even if it goes bad, simply unplugging it removes it from the Gy/Bk circuit.
Source: by ElKabong (Ken, El Kabong)

RABS Self Test Diagnostic Connector Location pic in an 88; "...it is next to the brake pedal which this is a picture of and is C111; It has the one wire that is black/orange.."
Source: by Jem270

RABS Self Test Diagnostic Connector Location pic in a 90; "...It comes out of a large loom under the dash, coming through the firewall, near the parking brake. On mine there are 2 similar connectors in that area, the correct one has only 1 black & orange wire running to it, & was hidden on top of the loom..."
Source: by ElKabong

VSS SENSOR Location pics in a 90 - transfer case tail housing
Source: by BlueBeast (The Beast), JP N) at SuperMotors.net

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Vehicle Speed Sensor (VSS)
The Vehicle Speed Sensor (VSS) is a small signal generator that is turned by a gear inside the transmission assembly. The Vehicle Speed Sensor produces 8 pulse per rotation which a stock computer assumes 8000 pulses per mile. The Vehicle Speed Sensor (VSS) is a variable reluctance sensor that generates a waveform with a frequency that is proportional to vehicle road speed. When the vehicle is moving slowly, the sensor produces a low frequency signal. As the vehicle speed increases, the sensor produces a higher frequency signal The Vehicle Speed Sensor (VSS) supplies this signal to the components that require vehicle speed information including the speed control amplifier for cruise control equipped vehicles and computer. The computer uses the VSS signal for emmisions contol programs and speed limiters. The emmisions programing can cause a manual transmission vehicle to stall out while decelerating if no VSS is used.

by Ryan M (Fireguy50)
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