A/C pressure sensor 5 Volt reference issues
A/C pressure sensor 5 Volt reference issues Hello everyone,
I'm looking to see if you guys can help me figure out the problem I am having. First off it started the other day while driving on the highway (3.5 hour drive). I turned the A/C on and it was working fine. I turned it off for awhile and went to turn it back on and it wasn't working. I kept trying to turn it on and finally it began to work again.
When I finally got home I checked the codes that were thrown they consisted of P0452 & P1639. I went to gearchatter and followed the diagnostics for the codes. As of right now I believe there is a short or something on the Gray 5 Volt reference wire on the A/C pressure sensor.
The wierd thing is when testing the Gray wire for "hot" using a test light nothing comes up but when I test it for ground using the test light it shows ground. I compared by testing the same way on my dads Vette which has the same sensor and color of wires. His has "hot" power when testing with a test light. Also there is only about .20 Volts according to my Digital Multi Meter. The vette has as expected Near 5 Volts.
I found a 5 Volt reference wire on the plug for the something to do with the smog I think. Anyways I cut the gray 5 Volt reference wire that goes into the A/C pressure sensor and spliced in the new 5 volt reference wire from the smog plug and the compressor clutch kicked in and A/C worked fine.
So obviously the issue is with the Gray 5 Volt reference wire that goes into the A/c pressure sensor plug. If anyone has an idea of what the issue can be or how I can fix the wire I'd appreciate your help!
Thanks in advance.
I'm looking to see if you guys can help me figure out the problem I am having. First off it started the other day while driving on the highway (3.5 hour drive). I turned the A/C on and it was working fine. I turned it off for awhile and went to turn it back on and it wasn't working. I kept trying to turn it on and finally it began to work again.
When I finally got home I checked the codes that were thrown they consisted of P0452 & P1639. I went to gearchatter and followed the diagnostics for the codes. As of right now I believe there is a short or something on the Gray 5 Volt reference wire on the A/C pressure sensor.
The wierd thing is when testing the Gray wire for "hot" using a test light nothing comes up but when I test it for ground using the test light it shows ground. I compared by testing the same way on my dads Vette which has the same sensor and color of wires. His has "hot" power when testing with a test light. Also there is only about .20 Volts according to my Digital Multi Meter. The vette has as expected Near 5 Volts.
I found a 5 Volt reference wire on the plug for the something to do with the smog I think. Anyways I cut the gray 5 Volt reference wire that goes into the A/C pressure sensor and spliced in the new 5 volt reference wire from the smog plug and the compressor clutch kicked in and A/C worked fine.
So obviously the issue is with the Gray 5 Volt reference wire that goes into the A/c pressure sensor plug. If anyone has an idea of what the issue can be or how I can fix the wire I'd appreciate your help!
Thanks in advance.
The reference voltage comes straight from the PCM. find that wire on the PCM plug and take a reading. If its still reading ground then the PCM is not supplying the voltage and the ground your reading is probably not from a short but from the ground on the other side of the variable resistor inside the inside the sensor.
Basically its one of only a few things. You've eliminated the sensor as the problem by splicing in another 5vdc reference so there's only two other possibilities....the PCM is not supplying the voltage (some thing internally wrong with PCM) or you have a broken wire between the PCM and sensor. There is also another possibility of something telling the PCM not to supply the voltage but without schematics I'm only guessing.
Basically its one of only a few things. You've eliminated the sensor as the problem by splicing in another 5vdc reference so there's only two other possibilities....the PCM is not supplying the voltage (some thing internally wrong with PCM) or you have a broken wire between the PCM and sensor. There is also another possibility of something telling the PCM not to supply the voltage but without schematics I'm only guessing.
Here is a link to the schematic just to be able to see things a little more clearly.
Tried to upload it to photobucket but it wouldn let me.
https://ls1tech.com/forums/attachmen...estion-ac1.gif
Tried to upload it to photobucket but it wouldn let me.
https://ls1tech.com/forums/attachmen...estion-ac1.gif
Ok thanks guys, I'll try and take a look at it tomorrow sometime.
Any idea what could of cause the PCM to go bad all of a sudden? Cuz Like I said the A/C was working fine, I turned it off for awhile, went to turn it back on and it wasn't working then about an hour later it started working again. All in the same drive and ignition cycle.
Any idea what could of cause the PCM to go bad all of a sudden? Cuz Like I said the A/C was working fine, I turned it off for awhile, went to turn it back on and it wasn't working then about an hour later it started working again. All in the same drive and ignition cycle.
*Update*
Ok I finally got around to borrowing a friends PCM yesterday and plugged it in and still no difference. The same symptoms occur.
So it must not be the PCM because the PCM I tried is a known working one.
According to gearchatter.com diagnostics for DTC P1639 it says to monitor the 5V on the AC pressure sensor while disconnecting each sensor connected to the 5V reference circuit one at a time.
If the voltage changes while disconnecting any of the sensors then that sensor must be replaced.
fleetmgr do you or anybody else, know what all sensors are on the 5V circuit? I believe the MAP, TPS, FTP, and of course the A/C pressure sensor are but don't know what else may be.
Here is the page from gearchatter I am using
http://www.gearchatter.com/viewtopic9327.php
Any other advice or suggestions on what could be my problem?
Thanks
Ok I finally got around to borrowing a friends PCM yesterday and plugged it in and still no difference. The same symptoms occur.
So it must not be the PCM because the PCM I tried is a known working one.
According to gearchatter.com diagnostics for DTC P1639 it says to monitor the 5V on the AC pressure sensor while disconnecting each sensor connected to the 5V reference circuit one at a time.
If the voltage changes while disconnecting any of the sensors then that sensor must be replaced.
fleetmgr do you or anybody else, know what all sensors are on the 5V circuit? I believe the MAP, TPS, FTP, and of course the A/C pressure sensor are but don't know what else may be.
Here is the page from gearchatter I am using
http://www.gearchatter.com/viewtopic9327.php
Any other advice or suggestions on what could be my problem?
Thanks
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Verdad Gallardo FTP sensor connector also is not putting out 5V. Everything else is though, (TPS, MAP, and the smog plug).
What could be causing the computers to not be giving 5V to these two sensors? (FTP and A/C Pressure sensor)
What could be causing the computers to not be giving 5V to these two sensors? (FTP and A/C Pressure sensor)
On the blue C1 connector at the PCM, pin #45 is the 5V ref for A/C pressure sensor. Same C1 connector, pin #46 is the 5V ref for the FTP sensor. Both wires are gray.
Check for your 5V right at the PCM. If you're not getting it, you need a new PCM. But if this is your finding, I would open the PCM and take a look before I buy a new one since the problem is with 2 adjacent pins.
Check for your 5V right at the PCM. If you're not getting it, you need a new PCM. But if this is your finding, I would open the PCM and take a look before I buy a new one since the problem is with 2 adjacent pins.
I have checked both wires coming directly out of the PCM and all I get is around 0.15 Volts.
Also I have tried another PCM in plac eof my original one and nothing changes. (This new PCM was working perfectly when removed from a friends car.)
Also I have tried another PCM in plac eof my original one and nothing changes. (This new PCM was working perfectly when removed from a friends car.)
TECH Addict
Joined: Jun 2009
Posts: 2,012
Likes: 0
From: Tulsa, OK
Been looking around in Alldata, and ran across this:
This is for my '96, but I'd bet there's no difference. A shot in the dark, but you never know.
Air Conditioning Evaporator Temperature Sensor
The air conditioning evaporator temperature sensor mounted to the heater and air conditioning evaporator module has a probe inserted into the evaporator which measures evaporator temperature and sends a signal to the PCM. Within the probe is a thermistor which varies output according to the PCM of the evaporator temperature so the compressor can be disabled before the evaporator freezes. The evaporator temperature sensor is a solid state device, do not attempt to measure resistance. Measuring resistance across pins cause sensor damage.
The air conditioning evaporator temperature sensor mounted to the heater and air conditioning evaporator module has a probe inserted into the evaporator which measures evaporator temperature and sends a signal to the PCM. Within the probe is a thermistor which varies output according to the PCM of the evaporator temperature so the compressor can be disabled before the evaporator freezes. The evaporator temperature sensor is a solid state device, do not attempt to measure resistance. Measuring resistance across pins cause sensor damage.
If 2 different PCM's give the same .15V on those wires, my bet is that you have corrosion on the connectors of C1 at those 2 pins.
Sorry to bump this thread after 2 years. This is only for people looking to figure out this issue. Try checking your wiring harness behind the ECM. A smaller group of wires in black conduit will be coming out of the firewall on the passenger side. Remove the ECU to gain access. There's a self tapping screw that this harness may have rubbed through. Open the conduit and repair wires if necessary and secure harness away from screw!
Teching In
Joined: May 2008
Posts: 12
Likes: 0
From: Stockholm-Sweden
I also have this code P1639 some days ago.
I just replaced the fuel pump some weeks ago, and it is a Fuel tank pressure sensor (FTP) to be found some where that i havent heard of. And that sensor can trig this P1639 .
So I may check that sensor now
I just replaced the fuel pump some weeks ago, and it is a Fuel tank pressure sensor (FTP) to be found some where that i havent heard of. And that sensor can trig this P1639 .
So I may check that sensor now
Registered User
Joined: Jul 2016
Posts: 2
Likes: 0
Chevrolet 5 volt reference issues - failsafe mode Hey bud did you ever find a fix for chevy 5volt reference issues with ECM, A/C, FPS and Tractioin Control issues? The local Chevy dealer here in Monroe, La have replaced MAP, Throttle Body, ECM and FPS sensor.....$2000 bill fixed it for one day....very nex day ir fell back into failsafe mode. Any help woud be awesome!! radiopeople1@gmail.com
For some reason I was not getting notifications for this thread. I don't quite remember exactly what the fix was as it has been quite some time since. I remember using the 5V reference from the smog wire temporarily. That worked for awhile, but now the car is wired back to the way it should be from the factory and everything is working as it should. I would follow the advice listed in the thread and work through it.
Good luck!
**edit: After thinking about it more I think I ended up replacing the FTP sensor and that corrected the issue but I can't say for sure.**
Good luck!
**edit: After thinking about it more I think I ended up replacing the FTP sensor and that corrected the issue but I can't say for sure.**
Last edited by nandos_z28; Jul 26, 2016 at 05:31 PM. Reason: possible reason
