P1682 and Engine Power Reduced - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 4 (permalink) Old 12-15-2016, 10:39 PM Thread Starter
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P1682 and Engine Power Reduced

Hey! I'll go ahead and apologize for the wall of text but I want to give as much info as possible, this is driving (heh) me mad. The car in question is a 2007 Cobalt 2.2L, automatic. It has 146k miles. Before all of this, when the car was on and only in park, the door locks would go a bit haywire, locking and unlocking randomly, I heard the relays clicking over and over. The key fob stopped working around this time too, thought it was a dead battery in the fob. Put it in drive and the door locks were fine, so I wasn't too concerned, but we did find some rat droppings under the hood. Wonder if one chewed some wires, but we can't find any damage. Otherwise, the car was perfect and good on gas. Did have a CEL, never checked it (no OBD scanner, I now know better, I promise!)

Now, the current problem(s)... I took it out last week, all was fine - parked, did an errand, got back in the car and suddenly it felt like it was stuck in 1st gear, and would shift up into higher gears seemingly at random, especially when letting off the gas. I went slow (15-30MPH) and made it home. Father's a retired mechanic, so I had him take a look. When he started the car the next day, the engine knocked real bad, was missing, and we got an "ENGINE PWR REDUCED" message on the dash board. It wouldn't move at this point. Now we're leaning towards it being an electronics issue and not a mechanical issue.

Both of my father's OBDII scanners would not read the car, so he had a friend with a better scanner come take a look, got P1305 (ignition coil pack 2?) among others (they didn't write them down! I think one was also P1682, not sure.) We got a new coil pack, installed it, and nothing changed, big surprise - but it did get rid of the P1305 DTC. So I picked up a cheap bluetooth OBDII reader on Amazon and used the Torque app, as we didn't want to bother the friend every time we needed to scan it. That connected and worked fine. We got the codes P0325 (knock sensor 1 circuit fault?), P1682 (ignition switch circuit 1?), and P0705 (transmission range sensor circuit malfuction?) We unplugged the ignition switch and plugged it back in (while the battery was connected, car was off - I'm certain that was a very bad idea.) After disconnecting and reconnecting the ignition switch, the car no longer starts. It cranks but does not start. We also had the ignition recall service done on the car this year.

We tested the battery with a multi-meter, didn't drop below 10.8 volts during the crank cycle. So we're thinking something shorted out when we unplugged the ignition switch, but we're not sure. The only code showing on the car right now is P1682, we had unplugged the battery for awhile to charge, as it went dead during the diagnostics work, so I guess that cleared the output. All fuses we know of look good (tested all with a fuse tester.) Under the hood and in the dashboard/console (the fuse box on the left panel in the passenger's side.) Also the 50amp fuse next to the battery tested good. Edit: I re-checked every fuse after this happened. Going to double check if I didn't put one back in the wrong place tomorrow...

I also noticed Torque shows the TPS at 34.9%, shouldn't it be 0 when the car isn't running? Would this prevent it from starting? I didn't notice this before we unplugged the ignition switch, but I wasn't really looking for it. From my understanding P1682 comes up when the voltage difference between the ignition 1 engine circuit (?) and ignition 1 powertrain circuit (?) has a difference of 4 volts or greater. I obtained a copy of ScanXL, ran PIDs GM.ENGINE.IGN1 and GM.TRANS.IGN1, which I'm assuming are the two ignition circuits in question (could be completely wrong) and they stayed at the same voltage, 12.4v - but ScanXL showed them going from anywhere from 3.2v to 25v when trying to start the car. Edit 2: reading docs again, 2.2L ENGINE CONTROL - and 0-25v IS the range for the ignition 1 circuit. Typical is 11.4. So I'm even more confused.

If my hunch is right, is this a dead PCM? As that sounds very expensive, I want to be 100% certain before having it replaced. We checked the connectors (with the battery unhooked this time...) and they all look super clean. Took off the top plate to check the PCB and it looked brand new. I was also digging in the manufacturer documents from this thread, it says the TPS position should be at 0 if the voltage supplied is less than 0.90v, did I read that right? I don't know how to test this, however, as there is no PID for the TPS voltage in ScanXL, can it be done with a multi-meter? Or point me towards another Windows program to try. I'll be testing every relay individually with a multi-meter and power supply tomorrow (if that's even the correct way to go about testing them.) Don't hear any clicking when trying to start the car, so maybe it's a dead relay, just a shot in the dark. We also haven't checked for any shorts, not sure how to go about that, nor ground locations. If the relays all check out I guess I'll dismantle the dashboard and check all of the wiring.

We're unsure of what to do now, can't find much information on any of this. It's out of warranty (obviously) - any thoughts? Bite the bullet and take it to the dealership, or continue trying to fix it ourselves? We're not super knowledgeable with the electronics part of the car, but I'm only out $70 for the OBII reader and coil pack thus far, and learning about this stuff is pretty fun. My only spare vehicle is a 1989 S10 that's been wrecked twice (not by me, hah, was a hand-me-down) and it's a hell of a ride every time I go to work! The more I dig into this thing the more determined I get to fix it...

Thanks for any input, glad I found this forum!

Last edited by kentu_; 12-16-2016 at 01:04 PM.
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post #2 of 4 (permalink) Old 12-16-2016, 02:49 PM
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If it's cranking batt good and starter is working. So for a running motor your missing spark and fuel. Check to make sure you have spark on all 4 plugs. Really easy since it's a inline 4 banger. Then check fuel rail to make sure your getting fuel

---------- Post added at 03:49 PM ---------- Previous post was at 03:47 PM ----------

Also thoroughly check fuses in engine compartment and bcm fuse block in passenger kick panel by console.
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post #3 of 4 (permalink) Old 12-25-2016, 11:55 PM Thread Starter
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Just an update: long story, but my car ended up going to a local service center where they have a dealership login. They found some bad ground points and it fired right up! Don't know which points were bad, though. No more CEL, and getting 28MPG highway currently, as advertised. Service center warned the ECU is probably on its way out. You can hear a relay under the gear select click - only when the car is in park and you hit the breaks, they couldn't figure that one out, so they labeled it as an ECU problem. If I understood them correctly, anyways. Door locks don't go crazy anymore though. That'd make sense, I guess - not looking forward to having the computer changed but I'll drive it until I get another CEL, haha. Throttle is still stuck at 34.9, not sure about that, either.

So was completely electrical. Thanks for the input above, although I didn't get to try what you suggested.
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post #4 of 4 (permalink) Old 12-31-2016, 08:25 PM
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Sounds like the "relay click" noise you're hearing under the shifter might just be the shift interlock that prevents the car from being able to be put in gear without you having your foot on the brake... if I'm understanding what you're writing correctly.
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