Hello - it's been a while since I've posted anything, but I'm having an issue with my 1990 Volvo 740 Turbo. The speedometer registers about 1/3 of the speed that I'm going so the max I ever see it register is around 25mph (aka 70mph) on the highway. It's very consistent, but consistently 1/3 of the speed.

What I've tried:
- cleaned the rear pins at the differential plug
- made sure the connection at the rear plug is solid
- removed instrument cluster and re-soldered anything that looked iffy

Based on what I've read my next purchase/course of action is to replace the sensor at the rear differential.

Note: ABS light is on.

Any other thoughts or ideas about this would be greatly appreciated. Rear sensors are a bit pricey.

I had the exact failure the below posters are describing where movement frayed the wires (and insulation). In that case, I had a normal speedo, then no speedo.

I believe that since it is working at all, and working linearly, the sensor and the wiring to it are not to blame. I would check the back of the cluster as was described. If the speed were jumping all around, I would think it's probably the wiring.

Good luck!

Since both the speedo and ABS are having issues, it sure sounds like the speedo signal.

I had the wires to the speedo sensor fray on both my 1990 and 1989. The wires were visibly frayed from years of movement near the connector. I got new connectors from Volvo and butt spliced (heat shrinkable) to the harness and it solve all the problems.

My symptoms were not consistent depending on how good a connection the frayed wires were making. If your's is always 1/3 perhaps it is the sensor though I believe that would be uncommon.

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Paul NW Indiana '89 744 Turbo 180K/ '90 745 turbo 145K

Since both the speedo and ABS are having issues, it sure sounds like the speedo signal.

I had the wires to the speedo sensor fray on both my 1990 and 1989. The wires were visibly frayed from years of movement near the connector. I got new connectors from Volvo and butt spliced (heat shrinkable) to the harness and it solve all the problems.

My symptoms were not consistent depending on how good a connection the frayed wires were making. If your's is always 1/3 perhaps it is the sensor though I believe that would be uncommon.

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Paul NW Indiana '89 744 Turbo 180K/ '90 745 turbo 145K

Hello,

Based on my experience on my 92 740, I experienced bad capacitors leaking on to the IC chip in the speedo gauge. This was visible after cracking open the cluster and removing the speedo. The IC chip in in the middle of the two plateds and the caps are right next to it. Lots of gunk around the pins on the IC chips that can cause lots of funny issues.

My experience is telling me that your sender is working as the speedo will come off of 0MPH but the electronics can't decipher the correct speed because of the bad caps and bridged pins on the IC chip. There is a write up in the FAQ about cleaning around the chip and replacing the caps. The IC chip is not available any longer. So the options are cap replacement and cleaning or junkyard speedo.

Crack open your cluster and see what you can see. Try a junkyard cluster, some yards will offer a 30 day warranty. There is also a write up in the FAQ about testing the sender with jumper wires.

John
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1990 740GLE 16v aw72 wagon 1992 740 Turbo aw71 wagon