I bought an ULTRA GAUGE, went to plug it in and the port was MIA, I fumble around and find it. Plug in the UG and it starts scanning and doesn't stop. I plug the UG into the Toy and it scans a couple of minutes and displays. So, it's not the gauge...
The gauge lites up and scans so there's power, but nothing else. Another odd and possibly related event, the temp gauge will read in the red, when the engine's at 195-200 on a new sending unit ( I also installed a VDO temp gauge) and I have a CEL...

All the other posts about this are pretty old and the most interesting fix was matching the replacement computer w/ the ABS module from the same donor.

I bought this rig w/ blown head gaskets and the OBD port had been fooled with, so who knows. That's most of the back round I have. I'm hoping some of you might have some insight on this. The nearest stealership is 115 miles away...
All help appreciated, thanks.

 

Where is the VDO picking up the temp signal?

The OBDII port has power, so fuse is OK.

The trucks runs, so the ECU must function at some level.

The OBDII reader can't connect to the ECU, which could be one of the other ECUs for a small system causing interference.

The OBDII port has a header, # C0286, under the heater fan. That can be unplugged, and a jumper run from just the ECU (cut from pin 20 on the header) to the wire going to OBDII port (cut from wire 16 on the header). So then you would have just engine ECU connected to it, and the other modules (air-bag, SLABS, cruise, ACE, tranny, and BCU) wont be there to interfere, if one of them is causing the problem... see attached.

 

Thanks, Savannah,
Good info. I haven't got started yet... I mounted the VDO water temp sender in the radiator hose "TEE" in front of the bleeder, I installed earlier. I posted a DIY w/ pix on it...somewhere...I'm not to good at this. I don't have any pix of the temp sender. I'll get a few and post them. There was one snag, I thought I was getting a grounded sender...NSL...So, currently, I have a jumper running to it, lol, but it works...Worst case, I'll tap the 1/8to 1/4" bushing and screw a ground to that. The whole set-up works really well.
Thanks, again

 

What kind of temp do you get at 50 mph or so, and how about at idle in traffic?

 

Hey, Savannah,
I only drove it briefly one afternoon...during which time it ran 195/200 around town, so, I jumped on the fwy, all grades from mild to moderate, it went to 205. On the steepest part, I put it in 3rd and wound it up a bit. It had no problems doing 75 on a grade which keeps alot of rigs to 65. It started to heat up at 210, I backed off, co-incidentally it was at the top of the grade. The next day I drove it, it started over heating...

Confounding variables: when I did the heads, I didn't have the radiator flushed, being as I couldn't do the block until it was back together. I flushed it with Prestone's super flush, after re-assembly. Next on the problems: no doubt, it had a previous head job...unknown how much was removed on the re-surface...I also re-surfaced, I hadn't much thought about it until I got the heads back and the chambers looked really small...if they had .20(or more) each time, this could now be a 11+/1 motor...further challenging an already challenged system...I'll have the system back flushed next week.

I'll post the results of the flush and wiring mods...

 

I had a water leak that cause the headers under the blower motor to corroad and caused the obd port to stop working. Definitely worth looking at that.

 

Thanks, wyrdvans,
I've been under the dash, all dry...I'm just having a trouble identifying which is the C0286, I'm thinkin' it's the one behind C0637. I just haven't gotten that far in my search through the RAVE to confirm...then, the task of implementing Savannah's instructions...lot of wires down there...
Thanks again