Chasing down the nasty p0748
05-24-2012, 08:41 PM
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Chasing down the nasty p0748 I have these 2 codes popping up on a 98 ls1/4l60 conversion. They did not appear after I put the car together first, but after tear down of complete car, paint, and re-assembly, they are present. Using the stock harness, and pcm with emissions deleted.
P0654 and p0748
p0654 is no engine speed signal and the p0748 is a trans code, pressure control solenoid circut. To test the p0748 I can test the trans pin connector for voltage/ohms, but from what I have read so far, the trans line pressure is determined via the pcm by throttle position, engine speed, etc., so do I need to figure out the p0654 first before I dig into the trans code? Engine speed is determined by the crank position sensor by the starter, correct?
Pulled the harness plug off the trans and checked ohms to the pressure control solenoid, came up with 4.6 ohms, acceptable values for the solenoid are 3 to 7 ohms, checked on pins c and d. So the solenoid is ok. checked pins on the harness, I am getting 7.9 volts on pin c, and d is a ground.
Next step, I got a complete trans harness with all the solenoids connected, plugged the harnes into that. Cleared all codes, then started car, and th p0748 popped up right away,as well as the 654. So just like checking the pc solenoid for ohms, this tells me that the p0748 is from the trans to the ecm.
Checked the wires from the plug to the ecm, they both look good, tested for continuity, both are fine. Whats next? Tomorrow I am going to take the ecm over to West Bend Dyno and have them go into the ecm and see if they can come up with anything thats wrong.
As for the p0654, changed the cam and crank position sensor, but have not started engine to see if anything has changed. Chased the whit wire from the ecm, pin 35 on blue connector, everything looked fine, no fraying or broken wire.
Will update with more as it comes.
Any input and past experiences would be appreciated.
P0654 and p0748
p0654 is no engine speed signal and the p0748 is a trans code, pressure control solenoid circut. To test the p0748 I can test the trans pin connector for voltage/ohms, but from what I have read so far, the trans line pressure is determined via the pcm by throttle position, engine speed, etc., so do I need to figure out the p0654 first before I dig into the trans code? Engine speed is determined by the crank position sensor by the starter, correct?
Pulled the harness plug off the trans and checked ohms to the pressure control solenoid, came up with 4.6 ohms, acceptable values for the solenoid are 3 to 7 ohms, checked on pins c and d. So the solenoid is ok. checked pins on the harness, I am getting 7.9 volts on pin c, and d is a ground.
Next step, I got a complete trans harness with all the solenoids connected, plugged the harnes into that. Cleared all codes, then started car, and th p0748 popped up right away,as well as the 654. So just like checking the pc solenoid for ohms, this tells me that the p0748 is from the trans to the ecm.
Checked the wires from the plug to the ecm, they both look good, tested for continuity, both are fine. Whats next? Tomorrow I am going to take the ecm over to West Bend Dyno and have them go into the ecm and see if they can come up with anything thats wrong.
As for the p0654, changed the cam and crank position sensor, but have not started engine to see if anything has changed. Chased the whit wire from the ecm, pin 35 on blue connector, everything looked fine, no fraying or broken wire.
Will update with more as it comes.
Any input and past experiences would be appreciated.
05-24-2012, 09:29 PM
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Unlike the shift solenoids, 7.9Volts on the PCS line is OK because it is actually a PWM (pulse width modulation line) and not a simple on/off line.
I would concentrate on fixing the the P0654 code first as that is the engine and the engine comes before the trans. Seems reasonable to hope that fixing that will fix the trans code too. Good luck.
I would concentrate on fixing the the P0654 code first as that is the engine and the engine comes before the trans. Seems reasonable to hope that fixing that will fix the trans code too. Good luck.
05-24-2012, 10:56 PM
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I am getting an engine speed reading on my Genesis, so the pcm is reading the correct rpms, the p0654 is just the code for the tachometer signal. Thanks for the input.
05-29-2012, 09:21 PM
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Well no luck with the guys at west bend dyno, the day after I talked to them, I called to tell them I was coming over and then they tell me they have no time to look at it, so I am not sure what to do about it now. Just going to drive it and see what happens. Worst case scenario is the trans gets smoked. Leaving for the power tour sat. morning, hope it holds up, or it will be an expensive trip.
