I bought a '96 suburban k2500 about 4 months ago. The ses light started coming on intermitantly. It has now decided to stay on. I read all the codes last night then cleared them. After driving about 80 miles the light is back on. I will read the codes again tonight. I have filled out as much of the checklist as I can and have included it below. Any help I can get would be greatly appreciated.
Thank you,
Noel

0. Describe in detail the problem you are having. Please be as descriptive as possible. SES light is on and seems to have lost some power.
1. Does the engine crank, or 'turn over'? Yes
1a. Does the engine start and run? Yes
1a1. If the engine does not start - Crack injector line (http://www.dieselplace.com/forum/showthread.php?p=2188140/lpost2188140): do you have fuel? Yes/No N/A
1b. Do you have a Wait To Start Light & the amount of time (seconds) lit. 8 to 10
1c. Ambient Condition (temperature outside indicate F or C) _____ ° 60°F to 80°F
1d. Engine Cranking speed (if you have an accurate tachometer). N/A
1e. Are you experiencing stalling? No
1f. If Stalling, describe (upon startup only, down the road, hit a bump etc) N/A
1g. If Stalling, do you notice loss of dash or instruments? N/A
-note if experiencing stalling,you must indicate PMD location in #24.

1h. Check turbo inlet and air filter for obstructions. Cone filters have lost disk and stopped air to turbo. New air filter.
1i. In a no-hot start, pour a bottle of room-temp water on the injection pump. Does it start now? yes/no N/A
1.1 Lift pump test (http://dieselplace.com/forum/showthread.php?t=39350)- describe results Not done yet
2. Service Engine Light while running?- on/off/intermittent On
2a. Service Engine light does glow during start/cranking/bulb check: Yes/No Yes
3. Model year 1996
3a. Odometer reading (indicate if in miles or km) 137,xxx miles
3b. Miles on major engine components if been replaced (example Injection pump) Less the 24,000 on pmd
3c. Indicate the model number on the Injection pump (starts DS4 or DB2......) UNK
4. Have you scanned for engine codes? (varies by pre/post 96) yes/no Yes
5. List exact results on engine codes (http://www.dieselplace.com/forum/dtc.php): P0236 turbo charger boost sensor A, P1656 Wastegate Solenoid Control Circuit, P1810 Transmission Fluid Pressure (TFP) Position Switch Circuit, P0711 Transmission Fluid Sensor Circuit range, and U3900 undefined
6. Air Filter condition (visual check) New
7. Fuel filter condition (freshly changed/condition unknown/mileage since changed) UNK
8. Condition of Battery (http://www.dieselplace.com/forum/l) terminal connections (removed, cleaned and tightened) removed cleaned and tightened
8a. Known condition and age of the batteries (http://www.dieselplace.com/forum/l). look new havent checked dates.
8b. Are batteries of differing age or are they a matched set? look to be matched set
8c. Condition of Major Grounds (http://www.dieselplace.com/forum/showthread.php?t=157085). (same drill as batt - removed, cleaned, retightened) not cleaned yet
9. Upon cold start, does the radiator (http://www.dieselplace.com/forum/l) hose get hard quickly? Yes/no not checked yet
10. Upon cold start, do you have excessive white smoke? Yes/no small puff of white smoke
11. Do you have excessive cranking time before the engine starts? not usually
12. Have you used the block heater, and does this effect engine starting?(only try for starting problems) no heater
13. During hard acceleration, do you have excessive black smoke? Yes/no some not sure if it would be considered excessive.
14. Do you have any unusual exhaust smoke issues? not that I know of
15. Turbo check out (http://dieselplace.com/forum/showthread.php?t=39368)- pass/fail Not done yet
16. Do you have an EGR on the engine? (An F or an S engine code 8th VIN digit) F
17. Indicate if you know if it’s a 1500, 2500, 2500HD, 3500, 3500HD. 2500 suburban
18. Indicate fuel that you are using: Bio-diesel, #2 Diesel, #1Diesel, SVO/WVO, other low sulfur diesel
18a. If running a VO (Veggie Oil fuel) setup, indicate details of your conversion (homemade, or packaged system) N/A
19. Are you using any fuel additives? If so, please list. Lucas fuel injector cleaner
20. Please indicate geographic region you are in: (example: Texas or Canada) south east PA
21. Do you have any service history available that might pertain to the problem you are having? unk
22. Please indicate any modifications to the vehicle that might help us diagnose better. relocated pmd
23. Upon unscrewing the fuel cap (http://dieselplace.com/forum/showthread.php?t=42338), do you have a large vacuum formed in the tank? yes/no did but replaced fuel cap
24. Location of PMD/FSD (http://www.dieselplace.com/forum/showthread.php?t=39436)? On the pump/remoted over intake/remoted out of engine bay (please specify placement specifically) remoted and mounted on top of left fender in engine bay
24a. If remote mounted, describe wiring harness (homemade or purchased from a vendor?) purchased from a vendor
24b. Indicate the location and condition of the FSD/IP grounding wire. unk
25. Are ALL glow plugs in proper working order as per this thread (http://www.dieselplace.com/forum/showthread.php?t=39182)? Not done yet

Need to know the codes.....

Does everything seem to return to normal after you restart the truck?
What kind of mods?
My truck will do this but only when I overboost it, It puts the truck into a limp mode that gives you just enough power to get home.
But this is a shot in the dark guess, for a more accurate answer we need more info.
Last but not least, Welcome to the Place'.

The codes are listed under number 5 of the checklist. I will post the codes that came back once I have a chance to scan them after work. It is stock except for the PMD relocation described under number 24. It doesn't seem to have lost much power just some under heavy accleration or going up hill. I may not have noticed the loss of power if I wasnt driving it every day.

First two codes sound like its not getting enough or too much boost, when you hit the go pedal pretty hard does it belch black smoke a lot? The other ones i have no clue how they relate... Lets see what the codes tonight entail...

When I hit the go pedal hard it does belch some black smoke I normally can't see it in the mirrors but someone following me can see it and tell I am driving a diesel. Being new to diesels I am not sure how much if any is normal.

It is normal for some black smoke, but a lot is not.... You need to check the wastegate, wastegate solenoid and vacuum pump. Make sure your getting vacuum from the pump, then see if your getting vacuum from the solenoid and then check your wategate actuator itself... What kind of miles are on this rig?

I have printed out and read the wastegate and vaccum pump test and plan to do them after work. There is a little over 132,000 miles on the sub. It was originally a state truck and was purchased by the previous owner a year or two ago at an action. He drove it maybe 2,000 miles in the year he owned it and had a remote mounted PMD installed. Since I bought it 4 months I have put 12,000 miles on it. I have had to replace the rear axle seals and rear brake shoes. Overall I am happy with the truck just want to get the little things fixed before they become big things.

Good plan, when you do a few simple reliability and performance mods these trucks are nice rides!!

Code P1656 Wastegate Solenoid Control Circuit is the only code that returned. I did the wastegate check and found the vaccum line going from the vaccum pump to the solenoid was not sealed at the solenoid. I sealed the vaccum line and erased the code so we will see if that fixes the problem.

The truck seems to be running better and no more SES light, knock on wood. Thanks for your help.

NP, good to hear its fixed!!

Love this easy fixes. Glad you found it.