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Discussion Starter #1 (Edited)
Speedo went out while off-roading a couple weeks ago. I wheel often in my truck, so not a unique scenario. Code is P0500. Tried the following:

1. Checked all fuses
2. Checked visible wire harnesses and connections. The connector on the driver's side ABS sensor is kinda busted up but still engages (see #5).
3. I measured the resistance across both VSS sensors on the trans. They both measured ~620 ohms and both change when metal comes near the end.
4. I measured the resistance across both ABS sensors in the rear. They both measured ~1100 ohms. I did not remove these.
5. I checked the resistance at the connector where both sensors go in above the diff. Both sensors read the same as the measurement at the sensor, therefore the busted connector in #2 is not an issue (it will be replaced regardless).
6. I bought a VSS sensor and replaced each sensor on the trans with it. Neither one made a difference.
7. I disconnected my Yellow Box Speedo Recalibrator, just in case that was bad. No change.

I don't want to replace the ABS sensors, they were $350 at AutoZone! :oops: Plus, since they both measure the same resistance I'm skeptical they're bad.

Some other info - I cut the wires for the front ABS sensors (suspension droop too much) and removed the ABS fuses years ago. The speedo has always worked fine like that, no check engine lights.

I'm thinking an issue somewhere in the wire loom? Any suggestions?

The FSM I have calls out some checks, but apparently somewhere along the line they changed the sensor type. I have two two-wire sensors. The FSM shows one three-wire sensor. So that's not much help.

Any help would be greatly appreciated!
 

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Discussion Starter #2 (Edited)
Some more troubleshooting:

1. Checked the voltage per the FSM (see attached pic). I get zero. But I don't even know if those are the right pin-outs for the 2006.
2. Jacked up one tire in the rear and put the multimeter clamps on the ABS sensor. I get a randomly fluctuating resistance of about ±0.5MΩ. It goes negative and positive. There isn't much change at a very slow speed, but spin the wheel about 90° per second and you get negative readings. I don't know how you get a negative resistance.
3. I get the same resistance for both sensors at the connector under the seat where the loom enters the cab as I do at the sensor. So at least the external looms are intact.

I think I'm going to order a couple ABS sensors and a new connector and replace them both. Hopefully that fixes things.

Any other suggestions, please chime in. Thanks!
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Discussion Starter #3
Pulled the rear ABS sensors. Lots of crud on them. Got excited that was the culprit. Cleaned them off and no dice.

I have new rear sensors and the rear sensor harness coming. If that doesn't work I'm at a loss what to do next.

20200514_154956.jpg 20200514_155215.jpg 20200514_154116.jpg 20200514_154210.jpg
 

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Discussion Starter #4
Replaced both transmission speed sensors and both rear ABS sensors. Also replaced the rear ABS harness with the damaged connectors. No luck.
Tore the instrument cluster apart and don't see any obvious signs of damage or burnt components. Running out of things to try now. Guess my next task is to tear the dash out and start tracing wires. I had a mouse problem in the engine bay last year, I suppose I could have a chewed wire back there. Thinking of ordering a new instrument cluster ($100) and seeing if that helps.

Anyone got any other ideas?
20200517_093618.jpg
 

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Discussion Starter #5
More troubleshooting. Found this check in the manual. Unfortunately, I don't have a oscilliscope so used a multimeter. I get 11.5V with the truck running. I don't see any fluctuation, but it may be too fast for my multimeter to pick up on it. Strangely, when I have the Yellow Box connected, it shows 14.5V.

I also get 0V with the connectors disconnected and checking that pin. Odd - you'd think there would be some voltage coming out.

I also realized the double cab wiring schematic is different than the access cab. I don't have the access cab wiring schematic, so that's not very helpful. But it appears at least some of the pin outs are the same.

Ordering a new instrument cluster. Guess I'll keep throwing money at it. :rolleyes:

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Discussion Starter #6
Tried a new (used) instrument cluster. No change.

So, I think that narrows it down to something in the wiring or the ECU. Crap.

Next stop is going to be Toyota. Let's see what they say for $150.
 
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