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Discussion Starter · #1 ·
Before everyone tells me to search the forum, I did but did not find the exact same situation. Help would be appreciated.

Recently completed - 4 inch lift installed, rebuilt F & R diffs with 4.56 gears, running 35 inch Toyo MT's. Recalibrated speedo to 599 which I found how to on the forums - thanks guys. Trans rebuild too.

My speedo jumps around 10 mph back and forth above 40 MPH. My ABS light turns on sometimes which I heard may be the problem but could also be the VSS.

Cruise control is working but obviously not well when the speedo is jumping around. Trans shifts seem to be also affected when the speedo jumps around especially when downshifting on the highway.

Anyone had/have this same issue and knows how to resolve it?

Thank you

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30,636 Posts
Before buying any parts;
This problem could be caused by a # of things;
bad vehicle speed sensor (VSS) (also called ABS,, DSS sensor) on the 8.8 (rear differential)/ or corroded Connector/ wires inside connector;
or cruddy/damaged tone ring in the 8.8.
bad 4WABS Module - It is located below ws wiper fluid/coolant recovery tank. So, the connector can be corroded by leaking fluid
bad PSOM (Speedo)
bad wiring/shorts /connectors from VSS at firewall, at 4WABS Module and /or at PSOM and then onto the PCM

The locations of the connectors along the path from VSS to 4WABS and up to Instr Cluster & PSOM are;
C404 VSS On rear axle sensor (A7) Terminals: 02

C205 LH rear of engine compartment, in safety wall (Fire Wall) Terminals: 24 In-Line

C202F & M LH rear of engine compartment, in safety wall (A8) Terminal: 7 In-Line

C119 LH front corner of engine compartment on 4WABS control module (E10),Terminals: 40

O/LB to:
C202F & M LH rear of engine compartment, in safety wall (A8) Terminal: 7 In-Line

C252 Programmable Speedometer/Odometer Module (PSOM), Behind top LH side of I/P, on PSOM (A7) Terminal: 12 Color: B at Pins 4

LG/Y to Splice S107 Engine control sensor harness, from C119 near T/O to G101 (G101 RH side of Radiator support); to PSOM Pin 5
C202 F and M
and spliced to Ground G100 (BK)
G100 & G104 (tied together in diagram) G100 @ LH front of engine compartment, on upper radiator support

G100 Serves Component:
Fuel Pump Module
Inertia Fuel Shutoff
Misfire Sensor aka crankshaft position sensor
Misfire Sensor Shield
Output Shaft Speed (OSS) Sensor
Powertrain Control Module (PCM), 5.0L

G200 Behind bottom of RH cowl panel
Serves Component:
Air Bag Diagnostic Monitor
Electronic Shift Control Module
Instrument Cluster
Programmable Speedometer/Odometer Module (PSOM)
Remote/Keyless Entry Module
Speed Control Servo/Amplifier Assembly

From PSOM Pin 7 (GY/BK) to Splice S246 Main harness, near T/O to speed control amplifier to
C185 PK/O @ PCM 5.0L Powertrain Control Module (PCM) LH side of safety wall, on powertrain control module (PCM) (C10) Terminal: 104 Color: GY
C185, 5.8L Powertrain Control Module (PCM) LH side of safety wall, on powertrain control module (PCM) (C10) Terminal: 104 Color: GY

C185 @PCM to C202 F and M
Splice 216 to Ground G200, Instrument Cluster ground is inside passenger side kick panel

and on to C185 @ PCM PIN 58 (GY/BK) and from Pin 46 to MLPS (TR) Pin 2
Verify PCM & MLPS wiring & Pin numbers using following WIRING DIAGRAMs by Ford via Steve83

1983 Ford Bronco PSOM picture |
PSOM diagram for '96 Bronco. '93-95 similar by Ford

"As the schematic shows, the VSS goes through some connectors, through the ABS computer, to the PSOM, then to the Speed control and the PCM. The PCM controls the shifting of the E4OD (Electronic FOUR speed OverDrive) transmission." by Mikey350

EEC IV Connector Pin LEGEND by Ryan @ Ford Fuel Injection

EEC IV 60 Pin Connector Pin Diagram by absent member Fireguy50 (Ryan M)

Cruise (Speed) Control Wiring Diagram in 93-96 with Pin Legend.

"...The correct PSOM vehicle speed signal to the PCM is an AC square wave that rises to 5 volts positive and drops back to 3 volts negative, with a frequency of about 120 Hz at 60 mph.
The sloping tops and bottoms on the waveform are normal, and don’t indicate a problem in the circuit..."
In a 92 F250, E4OD; Includes leaky capacitor on PSOM circuit board pic.

by Mike & Chris in Gear Magazine @ time. Transmission acted up again. This time we got a code! 452 - Ford Bronco Forum&txt=

Odometer & Keyless Entry Inoperative; Fuse 8 Overload, Possible Short In Circuit 54 TSB 95-14-11 for 94-95 Bronco & F Series; also affected Inoperative Courtesy, Map, Engine & Glove Compartment, Dome, Vanity, & Cargo Lamps & Inoperative Power Mirrors

Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19 @ Code Reader..... - 80-96 Ford Bronco - Ford Bronco Zone Early Bronco Classic FullSize Broncos]
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.
Run it around to heat the engine up and shift thru all gears incl Reverse. Then turn off all accessories/lights, etc.
Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch.
Do Key On Engine Off (KOEO) portion first.
And Post them here according to: KOEO & KOER

Check Fuses 8 & 18 in Cab fuse block (lower left of dash by driver's left knee)
If no 12 v on Supply Side of each; look in Power Distribution Box (Located under the hood on the drivers side fenderwell, on driver's side of the air cleaner housing)
and check MAXI FUSES J & S

My 96's same symptoms were erratic until the 4WABS Module's microprocessors finally burnt-out. I had one go bad and 2 yard Modules were also bad; so I jumpered the Module out as Turbo Ghost describes below.
To bypass the 4WABS module @ it's harness's connector & feed the ABS signal directly to the PSOM; "...jumper 14 (CKT 530, LG/Y) to 21 (CKT 519 (LG/BK) & 39 (CKT 491 (O/LB) to 22 (CKT 523, R/PK)...";
Source: by Turbo Ghost at How to bypass the 4wabs module for troubleshooting

Speed Input Signal Test @ PSOM in 93-96 Bronco; "...NOTE: Only wiring harness end of connector is to be probed. * Connect Rotunda Digital Volt-Ohmmeter 014-00407 or equivalent to Pin 4 (speed in ) and Pin 5 (speed in -). * Does the voltage increase smoothly and continuously from 0 to approximately 3.5 volts as vehicle speed increases from 0 to 48 km/h (0 to 30 mph)? OR: If available, a frequency counter may be connected to Pin 4 (Speed in ) and Pin 5 (Speed in -). Does the displayed frequency of the signal increase smoothly and continuously from 0 to approximately 667 Hz at approximately 48 km/h (30 mph)? OR: * If neither a voltmeter nor frequency counter is available, vehicle speed control may be used as a good indicator. If it works normally, then the speedometer module is at least receiving a speed input signal and the wiring and sensor & tone ring can be assumed to be good.
This is tuff to do; suggest using str8 pins to back probe the connector

For reference purposes:
PSOM Pointer PSOM Pointer Waiver TSB 96-21-11 for 92-96; "..The speedometer needle may waver and or a light surge may occur on some vehicles..." read more
Source: by Ford
This also addresses the tone ring & PSOM unit
EXCERPT; ISSUE: The speedometer needle may waver and/or a light surge may occur on some vehicles when speed control is used at highway speeds between 80-113 km/h (50-70 mph). This may be due to slight dents/chips in either the exciter ring or the Vehicle Speed Sensor (VSS) and air gaps between the VSS and the exciter ring.
ACTION: Replace the Programmable Speedometer/Odometer Module (PSOM) if required. New PSOM's come with increased immunity to system variability. Refer to the following Diagnostic Procedure for details.
BRONCO/F-SERIES - Perform normal PSOM diagnostics per Pinpoint Tests "H" and "J" of the 1996 F-Series/Bronco Body/Chassis Service Manual, Pages 13-01-30 through 13-01-32 and Pinpoint "B" of the 1996 Powertrain/Drivetrain Service Manual, Page 10-03-11.
Any slight dents, chips, etc., in either the exciter ring or VSS will create needle waver. Measure air gap between the VSS and exciter ring. It should be 0.38-0.51mm (0.015-0.020"). Check exciter ring runout per the same ring gear backface runout procedure of the appropriate model 1996 Powertrain/Drivetrain Service Manual, Section 05-00. Make sure the exciter ring is mounted correctly to the ring gear. If runout is more than 0.1mm (0.004"), perform the differential runout check per the procedure in the appropriate model 1996 Powertrain/Drivetrain Service Manual, Section 05-02A or 05-02D, to find cause and repair as needed

Tone Ring Inspection; "Take off the rear diff cover. Check the Ring Tone gear. It is located on the left hand side of the ring gear. Look to see if any of the teeth have been notched (from debris floating around in the diff.) Usually a spider gear. If the ring tone gear has been notched, it will need to be replaced to fix your speedo reading. Jack it up and rotate the tires to look for the teeth to be notched/broken/bent..."
Source: by Bighibbi at FSB
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