'94 940 speed sensor - wanted - P/N 1398321

DrJammer · Post by **DrJammer** » 14 Dec 2018, 19:33

Hey all, I am looking to help a fellow Volvo owner and I wasn't getting as many views in the classifieds. No speedo movement and the odometer is spinning like the Tasmanian devil. Trying speed sensor before going into the dash cluster.

Looking for this:

Hello MVS community - I am trying to locate a rear speed sensor for a friend. We are not certain of the speedometer issue. I have done some sparse diagnostics and would like to try swapping in a used, working speed sensor to see what happens.

I believe the P/N 1398321 can come from the following:
Vehicle Fitment: Volvo: 740 1989-92 | 760 1989-90 | 780 1989-91 | 940 1991-95 | 960 1992-97 | S90 1997-98 | V90 1997-98

I just don't want to buy a new one until I am sure that is the issue.

Please message if you have one for sale. Thank you

93Regina · Post by **93Regina** » 14 Dec 2018, 21:49

DrJammer wrote: ↑14 Dec 2018, 19:33odometer is spinning like the Tasmanian devil....a rear speed sensor for a friend.

Uh, unplug it....is there a change?

lummert · Post by **lummert** » 15 Dec 2018, 11:49

I'm thinking the cars you have listed use an impulse converter between the speed sensor and the speedometer. It's location on my 88 765 is under the drivers side dash near the kick panel. When you locate it you'll know as it has a red fuse plugged into it.

Post by **jimmy57** » 15 Dec 2018, 13:25

The 87 and 88 with ABS had to use a 96 pulse reducer converter due to the ABS using a much higher tooth count than the non-abs, 89 and later used 48 tooth tone rings and the speedo system was altered to use that input signal as is.

DrJammer · Post by **DrJammer** » 17 Dec 2018, 05:56

Hmmmm, I think I got that info from FCP. Will have to be careful upon ordering.

I unplugged the sensor and the odometer stopped rolling as well. Is it safe to say a new sensor is the remedy?

93Regina · Post by **93Regina** » 17 Dec 2018, 07:31

DrJammer wrote: ↑17 Dec 2018, 05:56Is it safe to say a new sensor is the remedy?

If the "Tasmanian devil's" rhythm is proportion to vehicle's momentum, his dance may be upstream.

Defuse ABS power, as one experiment....turn on lights, and change from low to high beam, as another experiment.

DrJammer · Post by **DrJammer** » 17 Dec 2018, 07:36

I am definitely not an electrical guru, not too familiar with the 94's, so I am not following completely.

speed sensor is unplugged and speedo doesn't work (duh), and odometer does not turn.

So I turn on the lights and fiddle with the high/low beams as an experiment. Am I seeing if there is a dash cluster issue?

93Regina · Post by **93Regina** » 17 Dec 2018, 09:19

DrJammer wrote: ↑17 Dec 2018, 07:36so I am not following completely.

Differenital's speed sensor "feeds" ABS and speed-o/odometer gauge. All that has been done so far is too show sensor's signal is working.

ABS unit may be creating a signal pulse...so remove its power. Also, each front-wheel sensor might be disconnected...I'd do both first.

On a Volvo semi-truck, flipping the headlights to high beam energizes speed-o to show false readings. So, with lights out...observe odometer's rotational speed at a given vehicle speed, then turn on low-beams, and observe, and then high beams.

lummert · Post by **lummert** » 18 Dec 2018, 12:28

If odometer was working with the speed sensor connected but isn't working with speed sensor disconnected the problem is most likely not the speed sensor. Perhaps the issue is the speedometer itself.

DrJammer · Post by **DrJammer** » 18 Dec 2018, 13:10

Thanks for the input so far. The car is across town, so I don't get to fiddle with it often. The fella drives about 1000 miles a year and was getting fired up when the odometer started churning.

I am not sure what to do after I try cleaning the front sensors and unplugging ABS and do low/high beam test.

I don't think I am up for soldering, repairing the speedo. Will a cluster replacement take care of this, if it is the speedo?