1998 S70 T5 unique battery drain at fuse #5

Bcbc · Post by **Bcbc** » 08 Sep 2018, 08:21

okay, so I've been using various online forums for years and have been pretty successful at finding fixes for almost every problem that I've have with my Volvos until now....
I'm experiencing a parasitic battery drain cause by a 200 ma draw at fuse #5 (Emissions fuse)
this is the fuse that supports the following emissions components:
7/15 – Front O2 sensor
7/82 – Rear O2 Sensor
8/18 – Canister Purge EVAP Valve
8/19 – Variable Valve Timing Solenoid (Camshaft Reset Valve)
8/28 – Turbo Control Valve
8/44 – EVAP Canister Valve
9/32 – PTC Resistor

I've unplugged every one and have traced the draw to the PTC resistor (air pre-heating nipple) . I have replaced the air intake tube, PTC and cleaned the connector, and its still drawing over 200ma when connected. I disconnect it and the draw goes way down to appropriate levels.

Can the ECU be faulty and sending power to this preheating unit? How difficult is it to find a T5M ecu to swap and try out?

It does have the air pump bypass diode in the ECU from previous owner.

Post by **RickHaleParker** » 08 Sep 2018, 09:03

9/32 – PTC Resistor?

What document are you using? 9/X in the Volvo Electrical wiring diagrams is heating elements, 7/X is sensors.
I'm seeing the PTC as 7/47.

---------------------------------------------------------------------------------

One side of the PTC is direct to ground. That would make for a pathway to ground if something else is leaking.

The problem could be leakage in the Fuel system main relay or it could be on fuses 2, 3 or 4 and the current is back flowing through 5 and the PTC. Try pulling the Fuel system main relay, Fuse 2, Fuse 3 and Fuse 4 while watching the current on Fuse 5.

You could put the amp meter across a disconnected PTC connector and pull Fuse 5 (Pulling Fuse 5 isolated the circuit from the rest of the car) if there is any current, the problem is on the Fuse 5 circuit, if not then it is one of the above.

Bcbc · Post by **Bcbc** » 08 Sep 2018, 11:36

I pulled the fuel main relay and fuses 2,3, and 4. still had a draw at fuse 5. Then I pulled the PTC connector and placed the meter in the connector and must have blown the fuse in the meter and only have the 10A option now. I'll need to get a new fuse to continue.
One thing I noticed is when I used the meter on DC volts, fuse #5 is reading 12.8v so it's getting full battery power sent to it, could the entire circuit be getting power and because the PTC is direct ground, it's staying on?

Bcbc · Post by **Bcbc** » 12 Sep 2018, 18:40

Another thing noticed.
I left an OBD WiFi reader sensor in the port and after sitting overnight I pulled the reader without ever touching or turning a key.
The reader was warm to the touch. Should the OBD port have power when the ignition is off?

Post by **abscate** » 12 Sep 2018, 20:39

Yes it does in some cars, and I think it does on Volvo.

WhatAmIDoing · Post by **WhatAmIDoing** » 13 Sep 2018, 09:05

OBDII will have power, but key must be in POSII for it to read anything.

Bcbc · Post by **Bcbc** » 13 Sep 2018, 09:26

Thanks, Just not sure about fuse #5 having power through it when the key is off. No reason the emissions sys or ac relay needs constant power.

WhatAmIDoing · Post by **WhatAmIDoing** » 13 Sep 2018, 09:46

I think you are right, something is grounding on fuse 5 that shouldn't be. I believe the only fuses that should be receiving power with the key off are for the alarm/anti theft system, and what keeps the stereo and dash computer memory. The ECU is also always receiving constant power.

Check the SAS bypass diode to ensure it is not touching something it shouldn't and is installed correctly.

Post by **RickHaleParker** » 13 Sep 2018, 20:35

I suspect there is nothing wrong with circuit #5. However circuit #5 is providing a ground path for a defect in one of the other circuits. That is why I outlined the test procedures above.

Bcbc · Post by **Bcbc** » 26 Apr 2020, 07:14

It’s been a while and I still haven’t figured this one out. The drain does not change when pulling any other fuses. It’s my son’s car and he’s been either plugging a battery maintainer in overnight and pulls out the #5 fuse when parked away from home and this has been a pta but keeps the battery charged. I haven’t pulled our the ecu yet so that might be done soon.