Odo/speedo

ckosmosis · Oct 22nd, 2004, 09:47 AM

I know the speedo problem on my 95 pickup has been adressed here 100 times. But what I am curious about is are the ODO and Speedo connected? My speedo works intermittantly and usually hovers somewhere between 10 and 30mph. Even at these slowly registered speeds I should see some change in the odo after 50 miles or so right? I hadn't seen any change at all, and then yesterday out of nowhere the dial moved by about 1/2 a mile, then it stopped again.

Any insight on the inner workings of the relationship between the odo and speedo for these trucks, or how the odo works, would be greatly appreciated.

Thanks,
-Chris

aaronford · Oct 22nd, 2004, 11:58 AM

As far as I can tell, the odo is driven by the speedo. My speedo would work intermittently causing a slight rise in odometer reading. But we are only talking 1000 miles in three years. I am going to try and post a pic of the unit.

ckosmosis · Oct 22nd, 2004, 12:23 PM

Thanks Aaron a pic would be helpful

aaronford · Oct 22nd, 2004, 12:26 PM

Quote:

Originally Posted by ckosmosis

Thanks Aaron a pic would be helpful

Hey, I posted the pic on my website. It is located at www.angelfire.com/extreme4/skidoolympique Click on Miscellaneous Pics and it will be at the bottom. The speedo needle is mounted to the brown pin just below the odo. It is surrounded by the spiral spring.

ckosmosis · Oct 22nd, 2004, 12:35 PM

Thanks for the pics, I have another question about your sticky. It says a wire goes to the ECU to set off the check engine light. If the speedo is malfunctioning should you get a check engine light? Because I don't and mine does come on at ignition so the light works.

aaronford · Oct 22nd, 2004, 12:39 PM

Just from looking at it, I would guess that the circuit board amplifies the signal sending it to the small motor (silver cylinder that protrudes from back) which drives the pin. The more volts, the more torque, and the harder it pushes against the spiral spring. The odo is driven by a small motor (white, mounted on the right side as viewed from front) and is mounted to the black plastic piece on the front of the main circuitboard. The speedo motor is also housed in this piece. I have removed the screws disconnecting the board from the speedo motor/odometer piece, but it will disconnect. It looks to be connected by the solder joints going to the speedo motor. If ya want to see it disassembled, I can probably desolder the joints. But I cannot see why unless it is for pure curiosity.

aaronford · Oct 22nd, 2004, 12:41 PM

Yup, you should be geting a CE light. It sends a signal anytime that you are going over 12 MPH. If this signal is not received but the ECU thinks it is going faster than that, it sets a code for the VSS. Mine would go out everytime the speedo started working.

ckosmosis · Oct 23rd, 2004, 11:27 AM

I am still trying to trouble shoot this without shelling out the money for a new sensor just yet. I pulled the sensor and the gear is in good shape so that isn't the problem. I pulled the head unit and there are now obvious burns or blown transistors. I did find a blown fuse for the engine control but that didn't change anything.

Heres what I find wierd. When the speedo is not working ( hovering between 10-30mph) the ODO will move 1 or 2 miles at random. But last night the speedo started working and I drove about 50 miles at 70mph on the highway and the odometer didn't budge.

There still isn't a CE light and when I did the diagnostic I got code 55 which is sytem normal. I am very confused at how this is all working.

-Chris

aaronford · Oct 24th, 2004, 02:14 PM

Just a thought, but if the speedo is working and the odo isn't or vice versa, then the prob is lilely in the head, not the sensor. Apparently it is still sending the vss info to the ecu, but isn't displaying properly. Sensors go for 35 and up, heads for 200 and up, unless you go used.