TeknoGodz

Hello all and thank you for your time reading and helping me with this issue.

I'm having a problem with my transmission. I'm getting D4 code 15 which is for Mainshaft Speed Sensor. The only CEL I'm getting is for the O2 sensor, which I will be replacing just need to get one of those special tools because the broken one is in there stuck like hell.

Basically the symptoms are after a couple minutes of driving the transmission just wont shift, I believe its staying in 2nd gear, but it doesn't shift at all after a few minutes. It might be 3rd gear it's getting stuck in, but I'm pretty sure it's 2nd. At 40mph it is about 3000 RPM, and at 55 it's about 4000RPM, and it just stays in that gear.

If I let the car sit for a couple hours and disconnect the battery or reset the ECM/TCM by pulling the 7.5a fuse then it will operate and shift normally for a few minutes, then it shifts hard and wont shift at all after that.

So in the manual it says to check the resistance and it should be between 400-600 for the Mainshaft Speed Sensor. I checked this at the plug and I'm getting a good resistance of about 560 at operating temperature. So the sensor is good. I also took out the sensor and cleaned it off, as I read that they are magnetic and can get dirty from metal fragments, but there was no metal on it when I pulled it out, looked just fine, so I wiped it off anyway and put it back in, same problem, no change.

The manual then says to connect "Test Harness D connector" to the wire harness that goes to the TCM, and check the resistance between D19 and D12 to see if the resistance is still between 400-600, which in essence will check the wires from the TCM to the sensor to make sure they're not broken or shorting out.

Is there any way to figure out what wires to check on the connector that goes to the TCM rather than using this Test Harness? I don't have the special harness that they're showing in the manual, and don't have access or funds to get one.

Anyone know what pins on the connector to the TCM correspond to the Mainshaft Speed Sensor, or anyone know how I can figure out which ones they are?

TeknoGodz

Okay, so I found another page in the manual that shows which wires on the TCM connectors are for what and I did the rest of the tests on the pages I attached.

1) The resistance is fine both at the MSS connector and at the TCM connector
2) There is NO continuity to ground on either wire.
3) There IS continuity from each wire at the TCM connector to the MSS connector.

So everything to do with the MSS is functioning perfectly fine... Now the question is do you guys think this is a transmission problem or a TCM problem...

Is it even worth spending the hundred bucks on a TCM at a junkyard to test, or should I just say **** it, save up some money and finally do a 5 speed swap... which honestly looks like it's going to be pretty hard but I think with some help I can manage. I've never swapped a transmission or removed one before, and the guides on the internet are honestly not well written...

holmesnmanny

If you're getting a code for the speed sensor then it's almost surely the sensor that's the issue. Just get another speed sensor off ebay or amazon for like $15. If the car doesn't know how fast you are going it won't know when to shift.

If somehow the sensor isn't even at fault, you only lost $15, but odds are it needs replacing anyhow.

This is a common issue.

I got one off amazon as well and about 50k later it's still working just fine.

If you really want to, you can pop open the tcu and the ecu and look for any burned or black spots. Obviously there shouldn't be any.

tech8

1. TCM code 15 is an electrical fault in mainshaft speed sensor circuit .

2. It is unlikely to be an issue internal to the transmission. Issue can be due to sensor, wiring, connector, or TCM.


Since your test found:

• Mainshaft speed sensor resistance within specs.
• With MSS plugged backed in, TCM harness connector wiring for mainshaft speed sensor shows resistance for MSS within specs.
• Harness wires (Wht/Blu and Orn/Blu) between MSS and TCM show continuity

Then it probably may be due to a faulty TCM.

TeknoGodz

I'll try to get a TCM at the junk yard when I have the cash, it just worried me that in the manual it says in the notes that code 15 could also be an internal transmission issue.

Is there any way to test the tcm or confirm that it is not a transmission problem in the mean time? I don't really have a hundred bucks to shell out on it, let alone something that might not fix it

Btw, I did open the tcm and found no burnt spots whatsoever