I'm being flashed

[Not a Tony]

Greetings all.

I've been lurking around this board for a while researching diesels, and now I've bought one. It's a '94 Chevy 1/2 ton extended cab 2WD with a 6.5 turbo backed up by an automatic. It seems to run well in spite of having 240k on the odo, and all the gauges are within the norms. My question is I keep getting a "Service Engine Soon" light. It comes on, it goes off. It comes on, it goes off. I can't really spot a pattern, but I have notices that if I'm cruising along and it comes on, if I back off the throttle, then get back on it, it usually goes off. Anybody got any ideas?

[Robyn]

Hello and welcome to TDP

The SES light is telling you "I HAVE ISSUES" :D

You need to pull up the codes from the ECM and see whats going on.
You can buy a simple OBD1 code reader at your parts store for a few bucks.

It plugs onto the data link connector thats right under the driver side dash area below the steering wheel.


Plug the little critter in and then turn on the key to the on position only (Do Not Start) The ses light will come on and then it will flash a series of flashes then a pause and then another series of flashes.
Such as "Flash flash flash-------- flash flash and then it will repeat this.

Count the number or flashes on each session and write that number down and then we can diagnose the issue.

The above example would be read as a 32

Once we know what the numbers are we can help you zero in.

With how you describe the way it acts it may be an EGR issue.

let us know

Robyn

[DmaxMaverick]

You could buy a code reader, but don't have to for a 94. If all you want to do is read the codes, you can do the same with a paperclip. Complete instructions on how to do this with a DTC list is HERE (http://www.thedieselpage.com/members/trblcode.htm).

[gmctd]

Try reading your DTC's as suggested - also test the vacuum pump output - should be

~26"HG at idle and at 2000rpm at the pump

~15" at idle and at 2000rpm at the wastegate solenoid

Low\erratic\no vacuum will cause Boost DTC 78 and one of several EGR DTC's on your 1500 "S" engine

You'll need to remove the TURBO DIESEL vanity cover to check this stuff out, btw..................

[Not a Tony]

Thanks for the info. For some reason, I can't read that page from here at work. I'll see if I can read it at home.

As far as the "Turbo Power" cover, it's already gone. No worries there.

[DmaxMaverick]

TheDieselPage article is available to subscribing members. Go HERE (http://www.thedieselpage.com/password.htm) for more subscriber information. www.kennedydiesel.com may still have the procedure posted.

[Not a Tony]

Okay. I checked the code and got a code 23. According to the code list, it appears to be an accelerator pedal position 1 circuit range fault. What does that mean?

Also, I noticed while I was doing this that the "Service Throttle Soon" light was illuminated. Is this related?

So what do I do now? I'm fairly familiar with gasoline engines, but this is my first diesel.

[gmctd]

Yes - if you take it to Autozone, they'll clear the code - if the same code returns, you'll need to replace the throttle APP sensor - might also try R&R'ing the connector, see if that clears it up - top of the accelerator pedal, pull the blue lock out, then remove\replace the connector - if no clear, replace the APP module - very unusual: we seldom see one of those actually go bad

[a5150nut]

Yes - if you take it to Autozone, they'll clear the code - if the same code returns, you'll need to replace the throttle APP sensor - might also try R&R'ing the connector, see if that clears it up - top of the accelerator pedal, pull the blue lock out, then remove\replace the connector - if no clear, replace the APP module - very unusual: we seldom see one of those actually go bad

When you do this a little contact or tuner cleaner fro Rat Shak helps with the conectors. I can't remember the exact procedure but IIRC, with paper clip in, turn on ignition, depress throtttle fully and cycle the brake off and on 3 times to clear codes. If I can find my book I will see if it is in there.

[Not a Tony]

I really appreciate all the help here. I haven't been able to make the fix just yet. Is it safe to drive it as is?

[DmaxMaverick]

I doubt you are hurting anything. More serious codes don't let the SES go out. Just drive it (or try to) and keep the SES off. Pull those codes ASAP. There's no reason you can't pull those codes at any time. 30 minutes or less with a paperclip will get all you need to know, for now.

[Not a Tony]

One additional thing I've noticed: the light stays off until the engine gets some heat in it. Is that consistent with the code that has been displayed?

[DmaxMaverick]

One additional thing I've noticed: the light stays off until the engine gets some heat in it. Is that consistent with the code that has been displayed?

No. If the APP has issues, it will be all the time, or randomly intermittent. It is remotely possible the module is being heated by the cab heater, making the issue more prevalent. You need to reset, and recheck the code(s) when it occurs. Usually when you have DTC's that occur when non related events happen, it will be an electrical fault somewhere. Usually a poor ground or bad battery(ies). Both are very common when the DTC's show up.

[gmctd]

Also, see what occurs in Cruise mode - the APP is redundant in Cruise.................

[Not a Tony]

Well, I set the cruise control and still got the SES light. I'm wondering if when I pulled the code, it was actually a 32 (EGR problem) and not a 23. I waited through three code 13's before the code 23 showed up, so I'm reasonably certain that was right, and I'm pretty sure I'm not a total idiot, but there is occasionally evidence to the contrary. I would think that EGR problems would cause some sort of driveability issues, but there have been none so far. It even started quite easily this morning in below freezing weather.

[a5150nut]

Well, I set the cruise control and still got the SES light. I'm wondering if when I pulled the code, it was actually a 32 (EGR problem) and not a 23. I waited through three code 13's before the code 23 showed up, so I'm reasonably certain that was right, and I'm pretty sure I'm not a total idiot, but there is occasionally evidence to the contrary. I would think that EGR problems would cause some sort of driveability issues, but there have been none so far. It even started quite easily this morning in below freezing weather.

Each code will flash 3 times per code then on to the next one.

[gmctd]

Autozone will read it for you - or you could get GMTDScanTech OBD1 pcware scantool - does everything the Tech2 dealer scantool does, except a lot more user-friendly, esp the price = ~125bucks, about 1/50th the price of the Tech2, installs\runs on your pc\laptop

GMTDScanBasic pcware may still be free, will read codes, same place - EnghMotorsdotcom - he's in the advertiser's section http://www.thedieselpageforums.com/adpeeps/adpeeps.php?bfunction=clickad&uid=100000&bzone=directlink&bsize=468x60&btype=3&campaignid=940477&adno=13&transferurl=http%3A%2F%2Fwww.enghmotors.com

Try it - you'll like it...............