1999 Volvo V70XC No Reverse

[KKiwi]

I have no scanner with me at the moment which is a problem. But I just went through that schematic you posted and I went out and started checking for continuity between the wires that were all connected to reverse and I found one of the wires had no continuity. I'll post a picture with the wire highlighted that has no continuity. Would there be any way to see what the wire is supposed to control?

[scot850]

It my be, but with your update, I would be looking at changing out the PnP switch and cable as it may be a bad wear spot in the PnP switch. If you have a junkyard nearby, it may be worth pulling a used one and trying it?

Neil.

[KKiwi]

It my be, but with your update, I would be looking at changing out the PnP switch and cable as it may be a bad wear spot in the PnP switch. If you have a junkyard nearby, it may be worth pulling a used one and trying it?

Neil.

Do you think I could just swap the pnp switch out with the old one on my old trans?

[abscate]

That wire is pulling down both A and B terminals to ground to implement reverse. It looks like those are CANBUS signals

Bingo, there’s your problem

[KKiwi]

That wire is pulling down both A and B terminals to ground to implement reverse. It looks like those are CANBUS signals

Bingo, there’s your problem

I wish I understood what that all means all I got from that was that I found the problem. So I just need to take apart my wire harness and follow that wire to find a short?

[scot850]

From looking at the wiring diagram, it looks to me like what abscate is saying (wiring is not my strong point) it there could be a wiring or bad connector between the TCU and whatever connector 3/71 is.

As to the PnP switch, they do wear out internally. We call it rowing the gear shift lever back and forth from P to 1 multiple times as it can sometimes clean the contacts in the PnP switch. The contacts do fail and the R is the most used. If your transmission was not working with the old switch, then it would point to the pnp switch not being the issue.

Neil.

[abscate]

I’ll clarify after I get the family off to work this am.

Ok

Disclaimer, I’m not an expert at this stuff. I’ll put it at 90% confidence level

I’ve labeled three things here. The green are the four solenoids that actually change things in th e transmission
The yellow is your bad line
The red is the guts of what happens at the gear selection lever

4CAD342B-CDA9-4F6B-BE24-D63B2BF0BAB1.jpeg (268.22 KiB) Viewed 474 times

S1 and S2 control the gears 1-4 by being in one of the four states that two on-off switches can have.
The SL and ST solenoids don’t shift gears, they control torque converter lock up and system pressure

OFF OFF
OFF ON
ON OFF
ON ON

The Volvo UK website tells which state is which gear is which state …

C2ADC5E2-477C-4796-8E4C-9EEDCE556E1E.png (530.27 KiB) Viewed 474 times

Finally,the Last one show what connects to what in R gear selection

1A4219A7-AD63-4E5D-92CA-83609E8DE818.jpeg (191.08 KiB) Viewed 474 times

Inthe R position , the lever connects the A and B terminals on the pin out connector to a terminal 31

X-X-X

Ignore the other two connections in R

Terminal 31 is a DIN standard for ground, so that means the pins on TCU that connect to A and B need to be grounded to engage reverse. They aren’t because of your broken yellow wire , shown on my diagram

[KKiwi]

I’ll clarify after I get the family off to work this am.

Ok

Disclaimer, I’m not an expert at this stuff. I’ll put it at 90% confidence level

I’ve labeled three things here. The green are the four solenoids that actually change things in th e transmission
The yellow is your bad line
The red is the guts of what happens at the gear selection lever

4CAD342B-CDA9-4F6B-BE24-D63B2BF0BAB1.jpeg

S1 and S2 control the gears 1-4 by being in one of the four states that two on-off switches can have.
The SL and ST solenoids don’t shift gears, they control torque converter lock up and system pressure

OFF OFF
OFF ON
ON OFF
ON ON

The Volvo UK website tells which state is which gear is which state …

C2ADC5E2-477C-4796-8E4C-9EEDCE556E1E.png

Finally,the Last one show what connects to what in R gear selection

1A4219A7-AD63-4E5D-92CA-83609E8DE818.jpeg

Inthe R position , the lever connects the A and B terminals on the pin out connector to a terminal 31

X-X-X

Ignore the other two connections in R

Terminal 31 is a DIN standard for ground, so that means the pins on TCU that connect to A and B need to be grounded to engage reverse. They aren’t because of your broken yellow wire , shown on my diagram

That makes a lot more sense now, thanks for taking the time to explain it all. I always thought I knew a lot with electrical but I guess I've just scratched the tip of the iceberg I'll see if I can't start following that wire today and see where it's disconnected. Here's to hoping this fixes my problem! Thanks guys!

[scot850]

Check for corrosion in connectors and oxide build up. Worth having an old toothbrush and electrical contact spray and clean each connection as you go. Although Volvo used good sealed connectors, sometimes when they are separated, they loose the little silicon gasket in them allowing moisture to enter and corrode away.

Good luck and thanks to abscate for the education. He knows how I love electrical.........!

Neil.

[KKiwi]

So I ran into a problem. I went out and started tracing the wire. According to the schematic it's a yellow wire so I found it and traced it. Turns out that the yellow wire coming off of the #2 lead from the transmission plug doesn't connect to the #54 lead into the TCU. It connects to the #64 lead. I spent like 20 minutes out looking at this to be positive but it's true. I have continuity with the yellow wire between #2 on my transmission side and #64 on the TCU side. On the bottom of the TCU on the schematic it has another wire coming off of #54 and going straight to ground. So I'm at a complete loss now