O/D light flashing

[jobaa]

sometimes i notice the o/d light on the end of the lever flashing. when it does my speedo is also dead. sometimes i pull over stop and restart the engine and it's back to normal other times it returns to normal while driving. it seems to perform o.k. when this happens but it's worrysome. thanks for any help. john

 

[whatabudro]

You have a transmission trouble code stored in your computer. Use a scan tool to pull the code. I would bet it's the speed sensor.

 

[jobaa]

it does show a speed sensor code #1211 but i have replaced it and the code still comes up. if i clear the codes it'll not show anything for a few days then pop up again. i believe that code will also indicate low trans fluid but it's at the proper level. i read that there may be a shorted wire in the loom. that's my next project i guess.

 

[whatabudro]

1211 isn't a speed sensor code

First digit structure is as follows:


P***x for powertrain
B***x for body
C***x for chassis
U***x for future systems


Second digit structure is:


P0*** Government required codes
P1*** Manufacturer codes for additional emission system function, not required but reported to the government



Third digit structure is:


Px1xx measurement of air and fuel
Px2xx measurement of air and fuel
Px3xx ignition system
Px4xx additional emission control
Px5xx speed and idle regulation
Px6xx computer and output signals
Px7xx transmission
Px8xx transmission
Px9xx control modules, input and output signals

The fourth and fifth digits designate the individual components and systems.

Anatomy of the Diagnostic Trouble Code

A DTC is made up of 5 digits. The figure below demonstrates the
composition of a DTC. With this information it is easier to trouble shoot a DTC
without knowing the description of the code.
X X X X X


First Digit
B-Body?
C-Chassis?
P-Powertrain?
U-Network


Second Digit
0-SAE
1-MFG


Third Digit
1-Fuel and Air Metering
2-Fuel and Air Metering (Injector circuit)
3-Ignition Systems or Misfire
4-Auxiliary Emission Controls
5-Vehicle Speed Control and Idle Control System
6-Computer Output Circuit
7-Transmission System
8-Transmission


Fourth and Fifth Digit
Fault 00-99


Types of DTC's
There are two categories of DTC's that apply to OBD II. They are listed
below with Type A being the more severe.


Type A
1. Emissions related.
2. Requests illumination of the MIL after one failed driving cycle.
3. Stores a freeze frame DTC after one failed driving cycle.
Type B
1. Emissions related.
2. Sets a Pending Trouble Code after one failed driving cycle.
3. Clears a Pending Trouble Code after one successful driving cycle.
4. Turns on the MIL after two consecutive failed driving cycles.
5. Stores a freeze frame after two consecutive failed driving cycles

 

[JLDickmon]

if you replaced the sensor in the rear pig, you replaced the wrong sensor..

the speedo is driven off the one in the trans tailshaft housing (up on top, damn near invisible on 4wd's)

 

[Tail_Gunner]

if you replaced the sensor in the rear pig, you replaced the wrong sensor..

I have to disagree, the speed sensor that provides input to the speedometer is indeed in the rear diff. Inside there is an exciter ring mounted right behind the ring gear.

I've been there, done that. Speedo would bounce between actual speed and 0. O/D light in handle would flash and the cruise control wouldn't work.

I replaced the speed sensor in the top of the rear diff and all was well again.

 

[firemediceric]

When my OD light was flashing it was due to the torque convertor falling apart and pieces of metal were sticking to the solenoid.

 

[action4478]

sometimes i notice the o/d light on the end of the lever flashing. when it does my speedo is also dead. sometimes i pull over stop and restart the engine and it's back to normal other times it returns to normal while driving. it seems to perform o.k. when this happens but it's worrysome. thanks for any help. john

Check the connection to the VSS . Look for broken lock tabs ,water, corrosion, breaks in the wires......

 

[COMPOSER]

I agree with TAILGUNNER. I switch mine out on my old 95. That solved the problem.

 

[JLDickmon]

I'm not gonna argue with you guys..

the sensor in the rear pig is the rear wheel speed sensor, not the VSS..

but if replacing it fixed your problems, crack a beer and call me Shirley