99 sts.. 1645 code

[99supersts]

Hello.. new to the site.. this is one of the only threads i could find while doing a google search so wanted to jump in.. im having the same issue with my 99 sts.. 1645 code.. ive replaced the purge solenoid, and ive checked all connections for tight fitment and even checked the fuse block for good fuses and everything appears to be good.. the CEL is still on for this DTC though.. any other ideas on what i could do to fix this? if the purge solenoid fixed my problem will it take a certain amount of starts before it will clear the CEL? ive only driven the car for about 20mins since fixing but ive tried clearing the code but it just comes right back on.. any help would be appreciated!!

[Cadillac Jim]

The 98-99 STS has a different platform than my 1997 ETC but I'll use my FSM because I think that the emissions circuitry is probably the same as yours.

DTC P1645, EVAP Solenoid Output Circuit, is treated on pages 6-612 through 6-614 of the 1997 model year FSM. There is a schematic there and a description of what happens to set this code. Basically, the ECS fuse (10 Amp) in the engine compartment fuse/relay center feeds the EVAP solenoid, and the other wire on the solenoid goes to the PCM. The PCM will throw this code when it doesn't see 12 Volts on the solenoid when it isn't trying to operate it.

There are at least three things that will cause the PCM not to see 12 Volts coming through the EVAP solenoid: a bad ECS fuse, a loose connector on the EVAP solenoid, or a bad EVAP solenoid. I would check these in that order. The ECS fuse is under the little plastic flap behind the air cleaner. It has a label, "Fuses."

[99supersts]

well on my 99 i have a fuse under the seat called.. fuel tank ventilation solenoid.. its a 10a, that fuse is fine .. the solenoid is new and the 2pin connector going to it looks fine, no broken wires or anything, pins arent damaged. as for any other fuses i dont see anything labeled EVAP or ECS..i dont see a fuse block near the air cleaner? mine are on the pass side under hood and under the rear seat..the pcm is up were the airc leaner box is though.

[99supersts]

well i caught the problem... it was the connector plug at the solenoid.. the wires looked ok , but after taking everything back apart again to re check it, i was pulling on both of the wires to make sure they were nice and tight in the plug.. the green wire i was able to stretch when i pulled on it so i knew the wire was broken inside the jacket.. took it apart and connected them together, the light went out as soon as i started the car.. thanks for the help!!

[Cadillac Jim]

Excellent!

On my car, the ECS fuse and many other fuses are under the hood behind the air cleaner. There is a big plastic cover that is held against the strut tower by a bolt that also holds a couple of hoses and a cable. There is a little black flap on that cover that is labeled "Fuses" (in black; it's written into the plastic, not a label) that lifts up to give access to about 15 fuses, 10 Amp and smaller.

You remove the bolt holding the big black cover to the strut tower and lift it up to access the Maxifuse block. Here are a whole lot of other fuses, including an array of 50 Amp Maxifuses. There are a bunch of fuses on the back of the back seat on the driver's side that are accessed by dropping the trunk liner; these are all about the suspension, radio, and other things. There are a bunch of modules on the back of the back seat, too.

On my car, there are a few other fuses scattered about the car. One on the steering column is for the air bags, for example. I don't know about any under the seat on my car. The platform (body and suspension design) on my car is nearly identical to that of the 2992-1997 Seville, but there was a platform change in the Seville for the 1998 model year.

Congratulations on a successful outcome. A broken wire is an unusual problem. Make sure that a tie-down isn't missing or some other such that allows the wiring to flex more than it should.

[99supersts]

yeah it was really weird how the wire was broken inside its rubber jacket.. but i dont have the same fuse locations as you i guess. i only have 2 fuse box locations with probably 30-40 fuses in each.. mixed with relays and all also.. pass side under hood behind the headlamp and then under the seat is my battery and another fuse block.. i have one issue left to deal with and its a c1712..open circuit LF strut.. they were replaced a few yrs ago with used ones so they cut and spliced the wire harness going to the solenoid in the strut.. guess im having a issue in the splice but im not having much luck re splicing and getting the code to go off.. might try soldering the connections and see if it makes a difference.

[Cadillac Jim]

C1712 Left Front Damper Actuator Open Circuit

Check the connector on the strut, too. If you have a multimeter, you might check the strut itself for an open circuit.

I'm assuming that you got OEM struts. If so, I'm wondering why they cut the harness instead of just using the existing connector on the new strut. Did you get constant-damping struts and a resistor for the wiring harness?

[99supersts]

supposedly it was a issue not long after he purchased the car from the dealer and they replaced the strut with a used one instead of new..why they spliced it im not sure but im guessing the connector on the solenoid itself doesnt come off so they were forced to splice?.. at least ive tried to remove the end on the solenoid itself and it feels permanently attached unless its just seized on there..but the previous owner told me when he would get the light on he would try to redo the splice and the light would go out for a lil while but then come back on so it must be the splice connection not making good contact.

[Cadillac Jim]

I just looked at a photo of a strut for your car on RockAuto. It has a cable about a meter long that has a connector on the end; the cable apparently doesn't come off the strut, normally. What seems to have happened is that the dealer cut the cable on the old strut *and* the new strut and spliced that cable, instead of unhooking the harness connection and plugging the new one in.

Good luck with the splice. I would use solder to get a sure-fire contact and heat-shrink tubing to get a good moisture seal. Look at what is needed to protect that part of the cable from debris, water and mud thrown up from the road, flexing from suspension motion, and physical contact. You might consider some plastic conduit from a hardware store to cover the splice.

[99supersts]

yeah thats what it was, from the splice to the connection it makes clipped to the body was just bad wire..i tried resplicing it 3 times and each time no success.. so i tried the 4.7k ohm resistor trick right at the harness and it worked so i new the problem was from the harness to the strut and didnt go any further then that..so i ran new wire from that harness down to the strut and the light went right off..

[Cadillac Jim]

Congratulations on your success.