1996 (corrected) 850 NA hot stalling

[850oldschool]

Okay, I've cleared the P1308 a couple times. When I switch to the Volvo specific codes it always comes back as an EFI-433/EFI-444 combination. So, I get the knock sensor code, as well as the accelerometer code when the car is sitting there idling.

I see from the wiring diagram that the negative wires from the accelerometer, the A/C pressure sensor, and the tank pressure sensor come together at pin 28 on the ECU, so there is some speculation about those other sensors tripping this code. But I still haven't read a story of somebody fixing their tank pressure sensor and getting rid of their P1308. Or swapping the A/C sensor and getting rid of the code.

Does ECU pin 28 connect to the chassis ground somehow?

[850oldschool]

I'm new to reading these wiring diagrams, so I can't tell if there is a wire which runs straight from pin 2 of the accelerometer and also a redundant wire through 23/221, or if it's an either/or situation.

[RickHaleParker]

I can't tell if there is a wire which runs straight from pin 2 of the accelerometer

Are you reading it old school (paper) or a electronics pdf file?

Pin #2 of the accelerometer goes straight to ECU pin #B28, It is the Accelerometer and A/C pressure sensor ground ... grounded through the ECU.

also a redundant wire through 23/221, or if it's an either/or situation.

No redundancy.
Four lines off that junction.
1. 4/28 TCM pin #22
2. 4/46 ECU pin #B36.
3. 7/17 MAF pin #6.
4. 17/13 OBD Socket pin #7.
It is a CAN bus.

[850oldschool]

redundant paths.png (169.56 KiB) Viewed 712 times

I'm reading a PDF scan of a paper manual, TP 3911202. I put red lines on the two current paths from the acceleration sensor to the ECU pin 28.

This is an ISO 9141 car. I didn't know they used CAN.

Last night I pulled and reseated the connector on the acceleration sensor, but I was still reading 5 volts on my scan tool and getting the code. Today, however, I'm getting 2.49 volts and that code is staying cleared.

[RickHaleParker]

TP3911202 is 1996 850.

This is TP3907202 1995 850.

[E Showell]

When I had a hot stall problem on a '96 850 it was traceable to a bad ground wire on the front cross member. Get down there and take a look, but trace all the wires with your hands. If I hadn't, I never would have found the clean break in mine.

[850oldschool]

TP3911202 is 1996 850.

This is TP3907202 1995 850.

2019-11-05 (1).png

This is a bit embarrassing. After I started this thread I went back and discovered that the car is a 96, not a 95. That 95 diagram you posted is considerably different.

[abscate]

We can go back and make all those folks look bad with a simple title change.

Sometimes the sea of information in the internet drowns us.

[RickHaleParker]

I put red lines on the two current paths from the acceleration sensor to the ECU pin 28.
Last night I pulled and reseated the connector on the acceleration sensor, but I was still reading 5 volts on my scan tool and getting the code. Today, however, I'm getting 2.49 volts and that code is staying cleared.

I found the same image in TP3911202. It is not redundancy it, is options. The EWD is written as one size fits all, that is cover all the markets and configurations. The dashed lines represent variations. In some configurations the Accelerometer is grounded straight to the ECM. In other configurations it is grounded via junction 23/231.

Because of a reevaluation of engineering and manufacturing finanaces in the 90s. You see less and less of that practice after the 90s because, they found it is more cost effective to use one part fits many then the old practice of trying to save money on parts. The saving from a reduction in handling overhead is greater then the savings in part cost.

[850oldschool]

We can go back and make all those folks look bad with a simple title change.

Sometimes the sea of information in the internet drowns us.

Not sure what your saying here. Could this thread title be corrected by a mod?

Rick, thanks for the background info! When I look at the diagram I'm quite skeptical that a fault with any of the other three sensors which are (potentially) bonded to the common ground at pin 28 could cause the accelerometer fault if the accelerometer ground is intact. It looks pretty simple: 5 volts goes out, and a fluctuating signal around 2.5 volts comes back.

Luckily the accelerometer code is staying away. Now I'm working on the EFI-433 code. If I clear it when the engine is running it comes back quickly, usually in less than a minute. The engine will run closed loop with normal short term fuel trim activity indefinitely until it's shut off. But when the engine is started with this code active it runs open loop.

So, this is where things get really, really confusing. The standard definition of a 433 code is "implausible output from the rear knock sensor". But the following list says the rear knock sensor is a 432 code:

https://www.matthewsvolvosite.com/volvo ... 96-to-1998

On that list a 433 code is "Front HO2S slow response", which actually seems much more likely to trigger a switch from closed to open loop operation than a knock sensor code. And just in case you aren't confused enough at this point and need a little more, on this list both of those codes are lumped together as P0331.