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Help troubleshooting boost sensor codes (P0238 & P1136) SOLVED
Am re-posting this to the 996 Turbo forum as I accidentally posted it elsewhere....
Been getting a couple boost sensor codes recently on my stock 2004 996TT with 25k miles which dont cause a CEL but is limiting boost in 1st gear and causes very erratic boost in gears 2-3-4-5.
P0238: 353 Pressure Sensor - Above Limit
P1136: Pressure sensors signal comparison charge pressure / ambient pressure - signal implausible
Done some searching and seems the boost sensor N75 maybe the culprit so I've ordered a new one which looks fairly straight forward to remove per this helpful DIY https://www.6speedonline.com/forums/...rging-fix.html
Has anyone else experience these codes (i've not seen P1136 on these forurms hence the ask) and have any feedback if the boost sensor (N75) was all that you had to replace? I cleaned up my MAP and MAP sensors and that didnt do anything to fix the situation and did a battery disconnect also with no improvement.
Thanks in advance for any feedback.... am planning to replace the N75 boost sensor and hopefully that fixes it but would again welcome any other suggestions should that not fix the issue. thx
thanks very much @Kevin looks like Chad_C and I have the same codes and situation... will check his thread to see if he has any findings or fixes.
still at a loss as to what's causing these codes (p1136 and p0238) and issues with inconsistent boost. Replaced the N75 sensor last weekend, plus MAF and MAP sensors and also did a battery disconnect over night and nothing changed.
I pulled the ECU tonight (10 min exercise on the cabriolets) and it looked fine, wiring harness was perfect and ECU pins clean no visible issues as I had concerns about the ECU being bad according to another thread on this similar situation.
Drove the car tonight and it shows inconsistent boost levels from gears 2-3-4-5-6 and no boost readings in gear 1 based on the dash display but using my ODB/iPhone app its showing 2psi in 1st gear and up to 16psi which cant be accurate since I'm on a completely stock ECU.
What else am I missing? Waiting for my indy shop to get me in hopefully within the next couple weeks so for now I'm trying to sort this out on my own. appreciate any insights...
N75 is not a sensor. It's a three-way solenoid valve.
Data logs would be helpful. As a minimum need RPM, injector pulse width, demanded boost, and actual boost.
This could be anything from stuck wastegates to a disconnected vacuum/pressure line to a huge boost leak.
N75 is not a sensor. It's a three-way solenoid valve.
Data logs would be helpful. As a minimum need RPM, injector pulse width, demanded boost, and actual boost.
This could be anything from stuck wastegates to a disconnected vacuum/pressure line to a huge boost leak.
@theprf thanks for your reply and suggestion... from your experience, is it common for the wastegates to get stuck if the car has been sitting for several months? Can they be fixed or if they're stuck do you find they typically require replacement?
My car has 25k miles but was sitting in a body shop not driven for basically 10 months and had the battery die as the shop was waiting for many months to get various body parts to fix some purely cosmetic issues so it just sat.
I'm in Chicago and trying to get over to Marek at Markski tuning to have him do a pressure test and check it out...
Yes. Get under the car and move the wastegates by hand with the engine cold. The actuator has a strong spring inside so you need to apply some force - one finger won't do it. The actuator pulls on the rod so move it the correct direction.
The other test for the wastegate actuators is to apply 0.5 bar pressure, which should cause the actuators to move a short distance (about 0.140 inch as I recall). This can be done at the N75 valve to test both at once. The hose from the N75 that disappears under the A/C compressor splits into two hoses and each branch goes to a wastegate actuator.
Yes. Get under the car and move the wastegates by hand with the engine cold. The actuator has a strong spring inside so you need to apply some force - one finger won't do it. The actuator pulls on the rod so move it the correct direction.
The other test for the wastegate actuators is to apply 0.5 bar pressure, which should cause the actuators to move a short distance (about 0.140 inch as I recall). This can be done at the N75 valve to test both at once. The hose from the N75 that disappears under the A/C compressor splits into two hoses and each branch goes to a wastegate actuator.
Super helpful. Thank you so much. I’ll get under the car tonight. Will search around the forums to see if there’s any write ups about manually operating the waist gates.
Yes. Get under the car and move the wastegates by hand with the engine cold. The actuator has a strong spring inside so you need to apply some force - one finger won't do it. The actuator pulls on the rod so move it the correct direction.
The other test for the wastegate actuators is to apply 0.5 bar pressure, which should cause the actuators to move a short distance (about 0.140 inch as I recall). This can be done at the N75 valve to test both at once. The hose from the N75 that disappears under the A/C compressor splits into two hoses and each branch goes to a wastegate actuator.
@theprf thanks again for the suggestion to check the wastegate actuator movement. I got under the car and both of them did move freely with appropriate effort which this other Rennlist actuator thread was helpful to showing where you manually pull on the actuator rod thats connected to the turbo.
Am at a loss at this point with what else to check so next up is a visit to Marksi and perhaps he can find a boost leak somewhere that I'm not finding?? thanks again for the help!
Check for air leaks from turbo intake. Should be no leaks.
replace several small rubber elbows . All rubber starts to fail 20 year old Porsche turbos. N75 :
Check for air leaks from turbo intake. Should be no leaks.
replace several small rubber elbows . All rubber starts to fail 20 year old Porsche turbos. N75 :
Cycle valve: 996-605-155-00
Venturi Tube Y: 996-110-652-70
964-110-950-02-M244
Secondary Air Injection Check Valve
996-110-318-02-M100
Throttle Body Seal
9P1-129-487-M253
Vacuum Line Connector ("L"4 mm)
996-110-652-70-OEM
Venturi Tube
996-110-649-71
Intake air hose
7PP-906-270-M244
Change-Over Valve for Air Injection
996-605-155-00-M244
Cycle Valve for Air Injection
996-110-135-70-OEM
Check Valve
@Chris996 thanks so much for sending this list of hoses and part numbers and I'll plan to start replacing all of those!
@theprf thanks again for the suggestion to check the wastegate actuator movement. I got under the car and both of them did move freely with appropriate effort which this other Rennlist actuator thread was helpful to showing where you manually pull on the actuator rod thats connected to the turbo.
Am at a loss at this point with what else to check so next up is a visit to Marksi and perhaps he can find a boost leak somewhere that I'm not finding?? thanks again for the help!
QUICK UPDATE - Well, my boost issue and couple codes has finally been FIXED after installing a new MAP sensor!!
I am very embarrassed to say that I had THOUGHT the MAP was replaced along with my MAF and N75 sensors which I commented about earlier in this thread but I came to learn that the buddy of mine who helped only with the MAF and MAP diagnosis actually forgot to install the new MAP sensor and instead jus cleaned the old one (CRC electrical cleaner) and left the new part in the box sitting in the car.
I was able to successfully clear the P1136 and P0238 codes after the new MAP install then drove it for about an hour and everything is running perfect full .7 bar and getting the standard boost across all gears (previously I was getting zero boost in 1st and very inconsistent boost in the other gears).
Amazing how such an inexpensive part that is so easy to replace can cause such problems!!!
Thanks all for your help to educate me here and finally get this sorted out!
10-05-2022, 06:13 PM
Help troubleshooting boost sensor codes (P0238 & P1136) SOLVED
