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DTC 1656

Big T

Big T

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Location
Fullerton, CA
My '99 started showing DTC P1656 this week. Basically, the SES light comes on when I turn the ignition on and waits for the Wait To Start light to go out. Then the SES light does not cycle off. I'm using my code reader to erase, but it continues to reapper, though not on every start.

P1656 Wastegate Solenoid Control Circuit

So this must be something to do with my Heath GL4 programming and the ATT turbo????:???:
 
Is it a new GL4 installed?

Did you unplug the wastegate solenoid? You dont have to have vacuum to it, but you should try leaving it plugged in electrically. Or you have shorted the wires somewhere.
 
buddy said:
Is it a new GL4 installed?

Did you unplug the wastegate solenoid? You dont have to have vacuum to it, but you should try leaving it plugged in electrically. Or you have shorted the wires somewhere.
Click to expand...

Bought the truck with the GL4 installed. I thought the wastegate solenoid was unplugged. I'll check that again. It's been fine up until the last week and I've had the truck since January.
 
Talk to Bill,

There have been a few "unique" 1656 prone trucks out there, mine was one, but eventually they figured the "bug" in it, (a problem with one of GM's updates not playing well with the reflashed PCM programming on some trucks) it happened when I was both with the GM turbo & the ATT turbo, so that is not the relationship.

Mine would only occasionally "hard code" mostly "soft code" stored as fault but never stayed on, this most associated when coding from S to F re-flashes. Talk it over with Bill he'll make it right.
 
I spoke with Bill at length. He said "the code parameters in the programming do not change, so something with the engine must have. Otherwise he would have known about this from the PO who installed it." He also said "It could be early programming, but it should have shown up like this from the outset."

To redress, I first saw this code once while lugging it (i.e. little boost) up a grade in the Rockies on the trip home from buying it. I purchased the code reader and cleared the DTC 1656. That was back in January of this year. I've driven the truck 11,000 miles since then and the code showed up once or twice in similar situations. Same thing, cleared it and it went away. Now this code appears nearly every time I go to start the truck. Normally the SES light will go on with the WTS (glow plug) light and go off when it's ready to start. Now it comes on, dims when I start and stays on, indicating a code thrown. It does not happen 100% of the time, but darn near that. Example, per advice here I unplugged the wastegate solenoid plug last night and when I started it this AM I did not get the code. I drove to the supermarket and when I came out and started it, the SES light stayed on and I got the code.

Bill Heath said I should load test the batteries (they're new this year) and test all the grounds using an ohm meter. I tested the grounds using the ohm meter and in each case I got 0.0 to 0.01. So they're fine. Also, it's a new 170 amp alternator and the voltmeter usually reads one tick past 14. Bill also said to pull the PCM and send it to him and he'll give it his most current programming for the ATT gratis. I'll pull it on a Sunday before I travel and have the wife send it by priority mail. Hopefully he can turn it around for me to reinstall the following weekend. Otherwise, don't really know what's going on.
 
Sounds like perhaps it was vibration dependent, like insulation rubbing over time. The PO probably knew about the intermitent issue.

I would be suspecting a short between wires on the harness or one of the wires to ground. It may not be seen sitting still, but if you shake lines see if shorts pop up. at work we would use a Megger Megohm meter to test insulation resistance with high voltage, but not a common thing to have laying around.
 
I wouldn't give 2 cents of worth to OHM readings on a ground. Heath uses voltage to check GP's, wonder why he says resistance for grounds.

Your batteries are rated at 650 Cold Cranking Amps each. 12.8 Volts becomes ~7 volts at the glow plug. This is due to the battery voltage drop and resistance under high current. the 1.5v AA battery in the ohm meter has limited value vs 2 12v Lead acid batteries in a high amp configuration.

Getting a good connection on the test lead is also a challenge for ohms where voltage is easier to get a reading on.

Quick and dirty ground test is looking for voltage across the ground wires with a load with 0.5v or more being a problem. 0 Ohms can become an open when cranking and the the loose washer in the connection is glowing white hot. load is headlights on, ac fan on high, engine off or running - Not while cranking and glow plugs not on.

Glow plug load can cause a corroded ground to heat up and fail.

Grounds or power supply to the computer can also cause havoc. Remove and reinstall all related fuses checking for corrosion. Pesky computer ground on back of engine...
 
WarWagon said:
I wouldn't give 2 cents of worth to OHM readings on a ground. Heath uses voltage to check GP's, wonder why he says resistance for grounds.

Your batteries are rated at 650 Cold Cranking Amps each. 12.8 Volts becomes ~7 volts at the glow plug. This is due to the battery voltage drop and resistance under high current. the 1.5v AA battery in the ohm meter has limited value vs 2 12v Lead acid batteries in a high amp configuration.

Getting a good connection on the test lead is also a challenge for ohms where voltage is easier to get a reading on.

Quick and dirty ground test is looking for voltage across the ground wires with a load with 0.5v or more being a problem. 0 Ohms can become an open when cranking and the the loose washer in the connection is glowing white hot. load is headlights on, ac fan on high, engine off or running - Not while cranking and glow plugs not on.

Glow plug load can cause a corroded ground to heat up and fail.

Grounds or power supply to the computer can also cause havoc. Remove and reinstall all related fuses checking for corrosion. Pesky computer ground on back of engine...
Click to expand...

Which one is the computer ground on the back of the engine? I can trace it on the '95, but not on the '99. BTW on the '95 we have it exactly where Bill said not to have it placed (bolt holding the Transmission dipstick tube), so I've instructed the son to move it.
 
ohm readings can be very useful. It was the appropriate application in this situation. He was not testing the batteries current capacity, just that he had good continuity, and not some rotted wire inside the insulation or corroded connections between terminal and ground.

If the computer ground was flaky you would likely have more problems. Need to investigate the circuit that the computer is saying is bad.
 
buddy said:
ohm readings can be very useful. It was the appropriate application in this situation. He was not testing the batteries current capacity, just that he had good continuity, and not some rotted wire inside the insulation or corroded connections between terminal and ground.

If the computer ground was flaky you would likely have more problems. Need to investigate the circuit that the computer is saying is bad.
Click to expand...

I need help investigating the circus, errr circuit. I pulled that wastegate solenoid plug while the engine was running. As I grabbed the harness, there was a slight hiccough in the engine. I could not repeat this though.

As for the ohm meter readings, I put one probe on the cable at the battery and one where it was connected at the engine. Other than that, I'm lost on this ground testing process. The extent of my electrical knowledge is check that it's connected and check the wire to see if the condition is good. That's it.
 
No problem.

With the truck off, and prefereably two people perhaps...

(1) place the ohm meter leads on each of the boost solenoid hareness pins (the cable end). Record ohm reading across the two pins. Shake the cable and the group of engine harness connectors behind the fuel filter manager and see if the resistance readings change and record.

(2) place one meter lead on one boost solenoid harness pin and one meter lead on the engine ground, record reading. Then shake the cable and the group of engine harness connectors behind the fuel filter manager and see if the resistance readings change and record.

(3) place one meter lead on the other boost solenoid harness pin and one meter lead on the engine ground, record reading. Then shake the cable and the group of engine harness connectors behind the fuel filter manager and see if the resistance readings change and record.

Its kind of annoying working on a circuit you dont even use. You could ask heath to disable all boost solenoid trouble codes and then cut the wires or pull the pins from the PCM harnesses.
 
I pulled the PCM and sent it to Bill Heath. Spoke with him today while on board my flight departing St. Louis. He said that the PCM was programmed for a stock turbo with a TM. The PO must have added the ATT after purchasing the GL4 programming. Bill will redo the programming (gratis) for the ATT. He said the ATT requires broader boost parameters and that plus change in weather, fuel formulation, etc would be enough to trip codes. I'll get it back next week. He asked me to drive it around for a week and then call him.
 
bison said:
I came the closests didn't i ;)
Click to expand...

Winner, winner, chicken dinner! :bow::partay::You_Rock_Emoticon::elf1

I knew when I was tripping codes on something which did not exist (i.e. wastegate solenoid circuit) that something was up with the programming. I reported this DTC when I first brought this truck home and someone here said it was due to the PCM looking for boost parameters that were not in line with the ATT. I will say that I'm learning a hell of a lot here on this site. If I had not been so far down the learning curve on this engine, I'd probably be in a 7.3 Powerstroke powered Excursion by now.
 
Big T said:
BTW on the '95 we have it exactly where Bill said not to have it placed (bolt holding the Transmission dipstick tube), so I've instructed the son to move it.
Click to expand...

This is where the grounds are on my '95. Where should they be? Any other bolt?
 
OK, I got the re-programmed ECM from Heath and it's installed along with the new 4" turbo back Diamond Eye Exhaust. Have driven the truck around. Towed the boat to the Davies Launch Ramp in Long Beach yesterday. Engine performs well. Highest spike on the turbo boost reading was 16 psi. Most of the time I see 12 to 14 psi when I step on it to pass on the Freeway.

So all is good BUT I still have the persistant DTC 1655. I can clear it with a code reader, but it immediately comes back. The SES light will be off after I clear it, but will come back on with the next restart. Code will register with the SES light off and engine running.

The braided ground from the engine to the frame on the passenger side was nearly frayed through. I replaced that when I installed the new downpipe. There is a second braided ground from the frame to the firewall that is frayed, though not close to breaking through. Did not replace that one. All grounds there relocated to the first intake manifold stud from the firewall. Driver's side ground is clean and good. Battery post mod is clean and good. Batteries are new this year.

Heath asked me to call him back after driving around for a week. Due to travel, I only have weekends. I've put about 150 miles on it with the new ECM. Pretty much know the DTC 1656 shows up every time I run it. I am at a complete loss on this.
 
Is your solenoid plugged in?....even though you don't use it?.....(WAG) Maybe you have a bad wastegate solenoid thats telling the PCM and there is your code.

This is if your WG solenoid is still plugged in.....If the Heath programing took it out of the "loop," then my (WAG) is N/A.
 
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