P 1656 ????????

[DA BIG ONE]

I've been going stir crazy w/this issue and hope somone can breack it down for me to better understand. I have no other codes.

P1656 Wastegate PWM solinoid driver circuit failed,
number of 'open' or 'short' faults detected=2 sets code,
wastegate PWM output voltage @ PCM does not follow s/w command.

What does this exactly mean, and what should I be doing to fix it?

HELP!

[JohnC]

The PCM must see a complete circuit from the 12 volt supply through the solenoid and back to the PCM's solenoid ground pin. When the PCM commands the solenoid on it looks at the voltage on the ground line. Likewise when it's commanded off. If it doesn't like what it sees it sets the code. A break in the wiring, a short in the wiring, or an out of spec solenoid (or resistor) will set the code. It may be sophisticated enough to tell if the solenoid is stuck, but I doubt it.

[DA BIG ONE]

The PCM must see a complete circuit from the 12 volt supply through the solenoid and back to the PCM's solenoid ground pin. When the PCM commands the solenoid on it looks at the voltage on the ground line. Likewise when it's commanded off. If it doesn't like what it sees it sets the code. A break in the wiring, a short in the wiring, or an out of spec solenoid (or resistor) will set the code. It may be sophisticated enough to tell if the solenoid is stuck, but I doubt it.

I ran up the motor to 2500 rpms from idle and solinoid circuit gave me a reading of 52.9% w/boost @ 3lbs, off boost I have 73.8%. Im thinking this is because I'm using Heaths stage 3 programing.

[DA BIG ONE]

I read somewhere that the later model L-65 (F) HD program needs to see 25Hg for wastegate solnoid circuit to function properly, would this still apply if I'm running a Turbomaster mechanical controller, or?

[JohnC]

I read somewhere that the later model L-65 (F) HD program needs to see 25Hg for wastegate solnoid circuit to function properly

The PCM doesn't monitor vacuum. It only cares that the boost is controlled and the solenoid circuit has electrical integrity.

[DmaxMaverick]

Any vacuum above 15" will keep the system happy. A pump performing at optimal can yield 26". 20-22" is typical. Less than 20" may indicate a failing pump. But, like JohnC said, the PCM doesn't monitor vacuum, only the electric components, and the effects of what the vacuum does.

[DA BIG ONE]

Any vacuum above 15" will keep the system happy. A pump performing at optimal can yield 26". 20-22" is typical. Less than 20" may indicate a failing pump. But, like JohnC said, the PCM doesn't monitor vacuum, only the electric components, and the effects of what the vacuum does.

Well, I guess I screwed up when I removed the vacuum pump way back when. W/O pump it won't be happy, or?

[DmaxMaverick]

Yep. If you are getting WG faults, and have no pump, that would explain it. Are you seeing the SES? If not with the BH computer, the code may be present, but w/o the SES. Poor programming, IMO, where the SES is masked, but the code isn't addressed. Seen it before with BH programs.

[DA BIG ONE]

Yep. If you are getting WG faults, and have no pump, that would explain it. Are you seeing the SES? If not with the BH computer, the code may be present, but w/o the SES. Poor programming, IMO, where the SES is masked, but the code isn't addressed. Seen it before with BH programs.

Guess I'm not going to get the DTCO KoKo to do its job w/the DTC1656 repeating every time the key is cycled 2 times.

[JohnC]

I still think you have an electrical issue with the boost solenoid circuit. The PCM doesn't give a hoot about vacuum. If the turbo master is controlling boost then the PCM will not set the boost code (P0236) and it isn't.

It is complaining about the voltage on the ground line of the solenoid. This tells me thet there is a break, a short, or an out of spec component between the battery and the switching transistor for the solenoid, inside the PCM. Maybe it's intermittent, but not likely if you get it immediatel after the second key cycle.

Or, it could be a fault in the programming. If the standard PCM doesn't fault, then it's the programming. If the programming eliminates the vacuum controlled wastegate, it should eliminate the fault, too.

[DA BIG ONE]

The stock ecm throws the DTC 1656 too so this eliminates the ecm as the problem. Also reminds me why I have a performance program in the other ecm, stock bites it.

So, now I checked the voltage at the solenoid and its variable with throttle movement, think GM calls for 8.0 volts w/key on at idle.

Checked resistance in solenoid and it is @ 40.0 ohms don't know what a good one should show, if any of you know please advise.

GM data on DTC 1656 points to a short, or open circuit as the culprit thinking of just making a new stand alone harness to this circuit and hope this fixes the problem.

As always I wish to thank all of who are assisting my effort to repair this circuit!

[DA BIG ONE]

I'm making a new harness for the 'wastegate solenoid circuit' I have a schematic of it but it is bridged to another circuit # S108 'power distribution schematics in wiring systems' > I need this schematic if anyone can provide it.

[DA BIG ONE]

I ran a completely new harness for 'wastegate solenoid circuit' no DTC or light.

The solenoid pulses real fast at idle and slows down as burb picks up speed, it shuts down at wot. I'm wondering if this solenoid is supposed to pulse like it does?

[gmctd]

PCM uses PWM on the solenoid to digitially regulate vacuum on the WG actuator, and also the EGR system, if ya got it - that's what the % reading is all about on the WG solenoid data point on the scantool - idle and cruising it's about 66%, so figuring 26" vacuum available at the pump, with mechanical losses and such, you should have ~15"HG vacuum at the WG at idle (0.66 x 26, iirc)

[JohnC]

It stops pulsing at WOT because it cannot control the boost. In a normal system this dumps the vacuum to the wastegate. The Heath PCM may be ignoring it, but it is setting P0236.

[DA BIG ONE]

It stops pulsing at WOT because it cannot control the boost. In a normal system this dumps the vacuum to the wastegate. The Heath PCM may be ignoring it, but it is setting P0236.

Have no codes now.

[JohnC]

Have no codes now.

Old programmer's adage: "Never trap an error you can't handle..."


Are you running the stock PCM? What are you measuring to determine pulsing? The rate should be constant; the dwell is what varies.

[DA BIG ONE]

Old programmer's adage: "Never trap an error you can't handle..."


Are you running the stock PCM? What are you measuring to determine pulsing? The rate should be constant; the dwell is what varies.

Using BH's program and I don't think I have the ability to measure the pulse and dwell unless my multi-meter can do it. My carcode gives me the % real time.

[JohnC]

Carcode will tell you what the PCM is calling for. The original programming doesn't adjust the pulse width from the default (~70%) unless certain parameters (RPM and fuel rate) exceed base values. Maybe what is happening is when those parameters are exceded the Heath programming just sets it to zero. Enough speculation, it's academic...

If you connect a dwell meter across the terminals on the solenoid you should get the same readings.

[DA BIG ONE]

I thank everyone for their input and now know a little more than I did before.