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Discussion Starter #1
Everyone,

So, the general wisdom is that activation of Limp Home Mode plus an OBD code p1530 indicates that a throttle body replacement is needed. I wish my current problem was that simple.

Here’s my story:
My 2008 Saab 9-5 w/128K miles ran like a champ all day. No CEL, everything is good. Parked in the driveway, went to bed.
The next morning I hop in, turn the key. She rumbled a bit as the starter cranked but would not run. CEL came on. I plugged in my code reader, found and erased code p1530. Popped the hood, reset the throttle body out of Limp Home Mode. I turned the key, she started. However, she would not hold a rev over 2000rpm. I held the accelerator pedal at about half way and she oscillated revs quickly between 2000 and 2750, back and forth, 2000 to 2750 back down to 2000 back up to 2750, repeat, repeat, repeat.

I replaced the throttle body with a known working one (I borrowed from one of my other 9-5 2.3Ts). Started her up, test drove, ran like a champ. Congratulated myself on a job well done!

She sat for six hours. I tried to start her, NOPE! Limp Home Mode plus p1530 code.
I considered that the electric connectors were not making good contact. So I popped off the connectors, inspected, found nothing obvious. Reconnected, reset LHM, and erased p1530 code. Tried to start, NOPE! Same as before.

Now the good news. I disconnected the battery. Waited a minute or two. Reconnected the battery. Success! She started right up, test drove, she ran like Secretariat.

To make this long story short...... my 2.3T is throwing code p1530 and activating LMH. The throttle body has been ruled out. Disconnecting the battery solves the problem. But the problem reoccurs when the car sits for any extended period of time.

Has anyone had and solved this problem in the past?

Thanks in advance for your help.
Chris
 

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Are you positive that you are resetting limp home mode correctly? I am not saying this in a condescending manner or anything...just making sure. Also there's a correct order of operations to this process. I am not sure if you reset limp home and then clear the CEL (or vice versa), but if you don't do it in the right order, P1530 will keep coming back and limp home will keep tripping.
 

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Discussion Starter #3
Problem solved.
I had a short in the wire leading to the Charge Air Absolute Pressure Sensor. There are 5 sensors on the 5V circuit the Throttle Body sensors use. A short anywhere in this circuit of 5 sensors can be misdiagnosed as a Throttle Body issue (P1530) and thereby cause activation of Limp Home Mode.
The strategy is to sequentially rule out each of the sensors on the circuit and check the wiring for shorts, crimps, broken attachments.
Below is information I copied and edited from the WIS, describing the 5V circuit components.

The following sensors are supplied with 5V from control module pins 69 and 46. The two 5V supplies are internally coupled to each other in the throttle body.
Manifold absolute pressure sensor (431 Located on the intake manifold.)
Charge air absolute pressure sensor (The absolute pressure sensor 603 is integrated with the temperature sensor 407 in one component. The 407/603 sensor is located on the charge air pipe.)
Differential pressure sensor, tank (a.k.a. Evap Pressure sensor 585, located on the fuel tank by the fuel pump.)
Pedal position sensors (Integrated into the throttle body 406)
Throttle position sensor (Integrated into the throttle body 406)
 
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