Hello! I just joined the forum and after having no luck searching for error code P1683B (Control Module Ignition Off Timer Performance) I decided to create this thread in hopes of finding some info and getting some help.

I'm working on a 2002 K1500 (Silverado 4x4) with the 4.8 liter V8 gasoline engine (VIN code V) that has 160714 miles. Over the past few years its Check Engine Light (CEL) has come on and then later gone off, with P0440A (Evaporative Emission System) being the main code found when the CEL was found on.

Currently the truck's CEL is off (the CEL is not on or lit), but stored as history codes are the following codes: P0300B (Engine Misfire Detected), P0440A (Evaporative Emission System) and P1683B (Control Module Ignition Off Timer Performance).

As mentioned above, the code I'm hoping about which to learn is P1683B (Control Module Ignition Off Timer Performance). The diagnostic tree for P1683 in Alldata simply says "Replace the PCM." No other diagnostics or things to check are listed, just to replace the PCM.

Other than routine maintenance (oil changes, new battery, replace worn brakes & suspension components) the only work this truck has ever received is a new ignition switch assembly (AC Delco part number 26098763) on 4/30/2009 at 120658 miles.

Emissions testing is coming up, so I plan on replacing the truck's spark plugs as a first step to address the misfire issue. Regarding the EVAP code, in the past the truck has been able to pass emissions by never letting the fuel level get below 3/4 full, as keeping a nearly full tank prevents the EVAP testing from occurring.

I have no record of the P1683B code ever existing on this truck before the new ignition switch assembly was replaced. I don't believe the two are related, but I wanted to mention that here in an attempt to provide as many details as possible. The first time I noticed the P1683B code was when the CEL turned on at 124937 miles on 8/12/2009, which is about 4 months and 4000 miles after installing the new ignition switch. At that time the P0440A code was current and active, while the P1683B code was a "history" code.

By the way, we use a Genisys scan tool (not a GM Tech II), so we do not have access to all the specific dealer tests mentioned in Alldata. However, the Genisys does store Failure Records, so I've printed the ones related to the P1683B code. They provide a short list of data saved at the time the error code occurred - I will list them below. The first number listed is from the first failure record, while the second number listed [in brackets] are from the second record. If there's no number in brackets that means that specific reading for the second failure record was the same as the first failure record:

Engine Speed = 0 rpm
TP sensor = 0%
ECT = 212 degF [216 degF]
Vehicle Speed = 0 mph
Barometric Press. = 28.99 inHg
Calc Engine Load = 0%
Commanded Gear = 1
Desired Idle Speed = 550 rpm [650 rpm]
Engine Run Time = 00:00:0hr
Fuel Tank Press SenV = 0.24 V [1.47 V]
Injector PWM Bk 1 Agv = 17.14 msec [16.74 msec]
Injector PWM Bk 2 Agv = 17.21 msec [16.82 msec]
Long Term FT Bank 1 = 0.0%
Long Term FT Bank 2 = 2.3% [3.1%]
MAF Sensor = 1.58 g/s
MAP Sensor = 28.05 inHg [28.94 inHg]
Short Term FT Bank 1 = 0.0%
Short Term FT Bank 2 = 0.0%
Start Up Coolant = 185 degF [239 degF]
TCC Enable Sol Comd = Off
Transmission OSS = 32 rpm

As I've said, we've been able to limp it through the emissions testing before, but it'd be nice to actually fix the truck. That being said, I don't really want to replace the PCM, especially since the truck has been cranking/starting/driving with no problems. To be honest I don't know if that P1683B error code has ever been active - as in the main reason the CEL turned on in the first place - or if it's one of those codes that doesn't turn the CEL on.

Any info/ideas/suggestions/questions? Thank you very much for reading and for any help anyone can provide.

 

The Genesis is a good unit. Have you cleared the codes to see if it repeats ? I personally won't replace parts unless I can repeat the problem. The other issues you had, might have caused the other code to trigger. If you have the other problems taken care of, I'd clear it out and see if it repeats. AllData is pretty accurate, if you can confirm their results, you might have to replace the pcm.

 

Good advice, and that's what I do each time: record the code(s), reset the code(s) and see if it (they) come back. Sorry, I should have said that.

With this truck each of the three codes all come right back after clearing them with the Genisys scan tool. I'll be installing new spark plugs after lunch, clearing the codes and then seeing what happens. Thanks very much for the reply.

 

I installed new set of spark plugs (AC Delco 41-110), cleared the codes and drove a total 121 miles at highway/city speeds (during which 9 engine crank/start cycles were performed). I encountered no problems during the drive, and the scan tool found no codes once I returned.

Emissions testing isn't until later this month, so we'll put some more miles on the odometer and see what happens. Thank you to MrDragon and everyone else who read my post.

 

Well, the truck failed emissions. What's puzzling is that during and after the miles driven after I changed the plugs there was no error codes. Then, of course, it fails the emissions test - not sure if it set a Check Engine Light right before the test or it'd been on for a while and nobody told me.

The vehicle inspection report from the emissions center says "Monitors Not Ready" and then lists "Evaporative System" and "Heated Oxygen Sensor." I'm certainly not going to throw O2 sensors on the truck without figuring out whether it really needs them, but it does I'll be happy to do so. By the way, our emission testing center checks the fuel cap during its test and our cap passed, so I am skipping the "try a new fuel cap" step.

Our Genisys reports the only current code as P0440A (Evaporative Emission System). "Fail since clear" codes are P0330B (Engine Misfire Detected) and P0440A. "History codes" are P0300B, P0440A and P1683B (Control Module Ignition Off Timer Performance), the latter code being the reason I created this post in the first place.

What I don't like is that a GM trouble tree for P1683B says "Replace PCM."

Again, if anyone has any advice regarding the P1683 (or even the P0440) I'm all ears. Thanks!

 

i hate to say this and i know how expensive they are but try and replace the 02 sensors
and when you failed inspections did they say why you failed that particular part
my car which is an 05 is throwning all of the same codes your truck is throwing and i know that it is the o2 sensors as my cats were plugged up and im pretty sure the o2 sensors went bad shortly after installing my thrush tubes
and i dont wanna fork over the 300 for all 4 sensors i need but i am going to evnetually have to

 

Instead of replacing the oxygen sensors I replaced the vapor canister purge valve (AC Delco 214-646). The reason I did this was because I found it to be loose in its socket/port on top of the intake manifold. Even though our scan tool showed that the original valve was in fact working, if there was a large leak (what diagnostics for P0440 included) a loose purge valve could be the culprit, and at a shade over $20 I decided to give that a shot. I installed it, cleared the codes and drove for 205 miles with multiple engine starts and no error codes. As a result, I took the truck back to the emissions testing center and.... it failed again.

When I was handed the failure report that I finally understood what the original failure report meant. As detailed in my first post, it said "Monitors Not Ready" and then the report listed the two other things. Those other things were two monitors that weren't ready. Originally it wasn't clear to me that it was telling me that two of the truck's monitors weren't ready - I mistakenly thought it was telling me there was a problem with the truck's EVAP system and the oxygen sensors.

This (the two "not ready" monitors) was verified with the Genisys, as I saw that the "Oxygen Sensor Heater" and "Evaporative System" monitors were set to "Not Ready." I spent a lot of time reading through Alldata to find out what actually happens when those monitors are engaged, or when/how their test begins, and then set about to try and complete the steps exactly.

When I turned on the truck the "Oxygen Sensor Heater" monitor read "Ready." As Alldata said the "EVAP Test begins once the engine coolant reaches a calibrated temperature", I backed the truck out of the shop to take it on a test drive, and within 60 seconds the monitor read "Ready." So I drove straight to the emissions testing center and the truck passed.

I wish I could say it was definitely the purge valve that did the trick. It could very well be what solved the problem, and for whatever reason it just may have happened that the truck hadn't completed its tests according to its desired drive cycle. Regardless, the truck passed emissions. I'll just have to wait and see whether the Check Engine light ever returns, and if so, whether that strange P1683 code reappears. Thank you to everyone who read and commented.