Thread: Car Suddenly Throwing Codes P0122 P0452 P1635 On Starting, Fuel Gauge Wacky

This all started a few days ago during our near zero degree weather. CEL on startup, can clear the subject codes and they wont come back until the next engine start up. Fuel gauge (tank is actually about 1/2 to 3/4 full) all over the place, goes randomly from empty with associated low fuel light, to peggged high full,and then back again. Also getting flickering low washer fluid level light especially on hills and on ramps but that may be real due to low fluid, but it seems I topped that off not long ago. Googling on those codes comes up with lots of hits of Pontiacs/other GMs throwing the same set of codes along with the fuel gauge problem, seems to be related to a problem with a 5V reference circuit that powers such things as the TPS, manifold pressure sensor, fuel tank pressure sensor. Other than the goofy gauge and CEL,car seems to run fine, although at times the tranny kickdown on hitting the throttle seems boggy. I'm thinking a bad grobnd circuit somewhere, but with so many hits on the same set of codes, coincident with the fuel gauge issue, hoping someone else has nuked this one out already. Tried searching on the forums here with no real help, in general, I have had trouble getting good hits on searches on here for many different items.

Chris, Stonington, CT
2001 GP 3.1 85K

Originally Posted by BillBoost37

Chris... hiya local!

Please take a second to search/google the codes and list out all the names of them.

P0122 Throttle Position Sensor Low Input
P0452 Evaporative Emission Control Pressure Sensor Low Input
P1635 5 Volt Reference 1 Circuit

From what I have read, and have been able to tell from a circuit diagram in my Haynes manual, there is most likely something dragging down the excitation voltage (the 5V Reference 1 circuit that supplies the TPS and the fuel tank pressure sensor, and most likely the fuel tank level sensor). Other postings around the internet show that the fuel tank loss of indication usually shows up along with these codes. One apparent common fault is breakdown of the 5V reference signal wiring insulation that can short it or otherwise drag it down. Going to try to track this down when the weather cooperates. In the mean time, car seems to run OK, once I clear the codes out after starting the car, they don't come back again until the next restart. There is indeed a certain amount of bogging on acceleration where the car probably should downshift but doesn't, it does accel OK if I manually force a manual downshift with the shift lever. I hope that the problem is a fault in the supply circuit within the engine management system module, if it is, I will likely build a small external supply ( temporarily, for troubleshooting purposed it could be as simple as 3 D cell batteries in series) if I cant find any faults external to the module in the wiring or the sensors themselves. One common thread that I see in the discussion of problems like this is that most people, professional repair shops included, immediately respond to a code from a specific component like a TPS by replacing it. In my experience as an electrical engineer and before that, as a bench rat in a TV and radio repair shop as a teenager, is that is far more common to have problems with simple things like bad wring or bad ground connections. BTW, the intermittent low windshield washer fluid light was indeed valid, it took nearly a whole gallon to fill it. I filled it a while back, and am surprised it was down so low, maybe there is a slow tank leak I am not seeing.

I have been looking for a schematic of the guts of the Power Train Control Module on the internet with no success, anyone know how to get one? Would be useful to fully understand for example how the fuel gauge works. Based on the obseved issues, it appears that it is also powered from the same 5V ref circuit as the evap emissions pressure sensor and the TPS. Interestingly enough, was talkingto a co-worker whose son also has a a 2001 GP, his is throwing the code for the evap emission pressure sensor (thats what their mechanic told them, wants to change it). He didnt know if there were any other codes involved, but he did say that he recently changed his oil and could now not reset the oil change reminder light. Whan I asked him how he did that he said it involved pumping the gas pedal 3 times rapidly. That was an A-HAA! moment, I'll bet he also is getting bad output from his TPS due to a root cause problem with the 5V reference power that feeds both sensors!

FIXED!!!! Chafed wires to the TPS cable got pinched into the air inlet rubber duct to throttle body intake joint at some point, wires chafed and shorted to the throttle body. Taped over the chafe, rerouted the wires, all codes cleared, gas gauge reads normal. NOT TO PREACH, BUT ALWAYS CHECK YOUR WIRING BEFORE YOU THROW NEW SENSORS AT AN ENGINE ELECTRICAL PROBLEM!!!