GIVING A CODE P 1635 - 1999 Pontiac Firebird

codes have several causes for showing up so post it all again with the code revealed if you want further assistance
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Of course it depends somewhat on the make model and year, but in general terms, code 335 is a problem with the crank sensor signal. The problem could be the sensor, the object the sensor is "seeing" on the crankshaft, or the wiring between the sensor and the ecm.
Code 1603 is a problem with the prom inside the ecm, or the connection between the ecm and the trans module.
Code 1635 could be a 5 volt reference problem or a problem with the axle differential.

Correct. It is a Shift Solenoid issue.

2004 lexus ls430 giving code p0756 and not shifting properly

https://www.fixya.com > ... > 2004 Lexus LS 430
Nov 20, 2019 - Here is the definition of the code. P0756 TOYOTA Description Shift solenoid valve B is turned ON or OFF by the Transmission Control Module (TCM) in response to ...
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This sounds like the ever familiar ABS modulator failing. However, VADIS doesn't list a OEM code with P1633 (it goes from 1632 to 1635). The 16xx codes normally relate to CAN bus or an individual controller. All ABS warning lights go through the ABS module, which is why you are seeing all three of those lit up.

P1684 Battery Disconnected in the last 50 Starts


P1389 No ASD Relay Output Voltage at PCM

Generally the code is for a problem with the 5 volt reference circuit which goes to several sensors. The reference is how the computer "watches' those sensors.
Could be a problem with the wiring harness or ground connections, or something internal with the PCM.

you need a haynes manual-go to a parts place and also ask an attendent--may hav a failin fuel system

The MAP sensor. Voltage from the MAP sensor is too low. Could be the MAP sensor is bad. Also check for any vacuum leaks.

Vacuum leak?

I had the same problem on my '02 Taurus, 3.0, V-6, 24 Valve engine. I replaced the plugs and plug wires which helped the problem but did not cure it. I then replaced the ignition coil (Motorcraft part # DG-485) which solved the problem. Has been running great since then...