1999 S70 Code ECM 4020, Cel, ETs..[solved by 9441116 brake position switch RR]

Post by **smacknab** » 12 Aug 2020, 15:17

Hi friends,

I've been having a reoccurring check engine and ETS light. Checking with my cheapo reader I've been getting codes p0452, p1041 p1081 in some order. I've been chasing this for awhile so my evap lines are all new (I find some that had burst), as are my evap purge valve and evap shut off valve. I swapped in a junkyard throttle body from another 99 NA which has run fine. I cleaned my MAF with approved MAF cleaner. I've checked and fixed all my negative battery/ground terminals, unless there's some in the trunk I don't know about.

Finally I brought it to a Volvo indie and they said it came back with code ECM 4020 - fuel tank pressure sensor. Has anyone dealt with this issue before? I'm not finding much DIY info online, and only Volvo sells the sensor for $250 (part #9155870). They advised me to check the confections/terminals so that's my next move. Just wondering if anyone else has some tips, since I really don't want to drop that kind of money on a sensor.

The main symptom I'm noticing is when coasting to a red light in neutral (the car is standard) that my RPM will dip to below idle, about 600 rpm. Once I make a complete stop the car will then return to normal. The other symptom is when filling up the car with gas, the hand pump will shut off consistently. Plus the reoccurring CEL and ETS light.

Thanks!

Post by **RickHaleParker** » 14 Aug 2020, 05:58

Diagnostic trouble code (DTC) ECM-4020 is stored if the engine control module (ECM) registers a fault in the signal cable to the fuel tank pressure sensor.

Clean the connectors and check the wiring harness for shorts and opens before replacing that expensive sensor.

Post by **RickHaleParker** » 14 Aug 2020, 06:12

P0452 is ECM-4020.
P1041 is the Brake pedal sensor
P1081 is Immobilizer communication. Check Antenna ring, wires and connector.
.

Post by **smacknab** » 14 Aug 2020, 07:59

RickHaleParker wrote: ↑14 Aug 2020, 05:58 Diagnostic trouble code (DTC) ECM-4020 is stored if the engine control module (ECM) registers a fault in the signal cable to the fuel tank pressure sensor.

Clean the connectors and check the wiring harness for shorts and opens before replacing that expensive sensor.

P0452 is ECM-4020.
P1041 is the Brake pedal sensor
P1081 is Immobilizer communication. Check Antenna ring, wires and connector.

Hey Rick,

Thanks for the further help! I just got some electrical connector cleaner and i'm gonna climb in the trunk and check those wires today.

The immobilizer issue pops up sometimes if i sit in the car a bit with the key in pos2 before i start the engine. When i do that either it wont start or it starts and immediately shuts off. Always starts at the second try. I was gonna swap the ring with a junkyard unit but i thought that the computer might have to be programmed to accept it or something, is that the case?

Is the brake pedal sensor something i should be worried about? do you think thats a connector issue as well?

Post by **smacknab** » 14 Aug 2020, 11:26

Got back there and pulled the connectors on the black bracket one by one to clean them with electrical connector cleaner. Also found some spider webs in the little white tube and cleaned those out with a pick.

Definitely smells a little like gas back here, without even having the car running, so there could be a leak somewhere? Or is that normal by the fuel pump?

Also from taking this apart and being back here, it looks like the actual sensor itself (#7 on the diagram) is not accessible from the top and I'd have to drop the tank to get to it?

Otherwise I didn't notice any frayed wires or broken connections back here.

Post by **RickHaleParker** » 14 Aug 2020, 12:10

smacknab wrote: ↑14 Aug 2020, 11:26 Otherwise I didn't notice any frayed wires or broken connections back here.

Just looking does not cut it. Break out the Ohm meter and measure.

Checking for shorts is easy. Just check for continuity between two wires that should not have continuity. If none, the wires are not shorted.

Opens is a little harder. On one end short the two wires. Then check for continuity at the other end. If none one of the wires is open.

Post by **smacknab** » 14 Aug 2020, 12:34

So i unplug the battery, disconnect the correct plug on the black bracket in the picture and test each side of the plug? I'll have to look up a guide for testing as I'm not following 100%

Post by **RickHaleParker** » 14 Aug 2020, 15:39

For shorts you pull the plug and test for shorts between each possible pair of wires in the harness. Keeping in mind a ground to a ground will show as 0 Ohms.

If you don't have fundamental electronics knowledge you will need to have somebody test the wiring for you. If this is the case you are not alone. Plenty of professional automotive mechanics do not fundamental electronics knowledge. That is why automotive electronics specialists get the big bucks.

Post by **abscate** » 14 Aug 2020, 16:13

The ecm code for leaving the key in is normal. You Run Into this if you do the immob key under the dash trick

Fuel tank drop in the FWD cars is about an hour. Empty it first of course. 10 liters of fuel is ok

Post by **smacknab** » 14 Aug 2020, 16:42

abscate wrote: ↑14 Aug 2020, 16:13 The ecm code for leaving the key in is normal. You Run Into this if you do the immob key under the dash trick

Fuel tank drop in the FWD cars is about an hour. Empty it first of course. 10 liters of fuel is ok

Welp I guess I found my Saturday plans! I'm assuming I can drain the tank by disconnecting the fuel filter with the back jacked up?

Rick I'll follow your advice and pull out my multi-meter to test both ends of the cable. I'll test the fuel tank pressure sensor cable to it's disconnect and look for the diagram where to test the other side of the cable