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P0785, P0783, P1860, Tranny or Ignition switch???

PedroJ

By PedroJ
in 2000-2014 Silverado HD & Sierra HD

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PedroJ New Member

PedroJ

Posted
Posted (edited)

Please Help. We're working on a 2001 Chevy Silverado 2500HD.It was stuck in limp mode. We first got the P0783-85 codes, so we replaced both shift solenoids, as well as the wiring harness. Still shot the same codes and was stuck in limp mode. So we replaced the transmission. Still didn't work. Now it's pulling up P1860 and both shift solenoid again. Also I realized it was shooting these codes before I even put it in gear. And that's what makes me think it's the ignition switch. Any help at all will be greatly appreciated and save my sanity.

Edited by PedroJ
Motor City Rick Enthusiast

Motor City Rick

Posted
Posted

Starting with the P0783 code:

 

Potential causes of a P0783 code include:

  • 3-4 shift solenoid failure
  • Electrical short to power - pinched wires
  • Electrical short to ground - pinched wires
  • Open in power or ground circuit wiring - disconnected or loose connections
  • TCM or PCM internal failure

Potential causes of a P0785 transmission code may include:

  • Damaged or defective shift timing solenoid
  • Dirty Automatic Transmission Fluid (ATF)
  • Low ATF
  • Obstruction in ATF passages
  • Broken or damaged wiring harness
  • TCM issue
  • ECM issue
  • Pin/connector problem (corrosion, melting, broken lock tab etc.)
P1860 CHEVROLET - TCC PWM Solenoid Circuit Electrical
Possible causes
  • Faulty Torque Converter Clutch Pulse Width Modulation (TCC PWM) Solenoid
  • Torque Converter Clutch Pulse Width Modulation (TCC PWM) Solenoid harness is open or shorted
  • Torque Converter Clutch Pulse Width Modulation (TCC PWM) Solenoid circuit poor electrical connection

 

Looking at all the codes, ...and their "commonality" I'd look at "all" the electrical connections going in and leaving the trans for corrosion, rust, broken pins. See if the wire harness is pinched / sliced back to the ECM. Another biggie, I need you to check both sides of every fuse in this truck. That includes any power distribution fuses. If any fuse is blown, that is a short to ground.

 

First, clear all codes, turn key on to get vehicle power, what codes returned???

 

No codes, start motor and let warm up. What codes now???

 

Report what codes you have at this point not putting the truck into any gear.

 

Now wiggle any wire harness from trans back to the ECM truck power on, motor not running. Check for new codes. Look for possible shorts to ground or severed wires.

 

You said you replaced the wire harness, ...what wire harness??? Wire harness for this ECM to trans is over $1000. I'm confused???

 

It is not an ignition switch issue, I'm leaning towards a short to ground or open circuit at a connector.

  • Like 1
davester Senior Enthusiast

davester

Posted
Posted

Yeah, it looks like an electric and/or tcm issue. I wouldn't expect a problem with the ignition switch/wiring harness to throw these codes...

Supreme Pizza Senior Enthusiast

Supreme Pizza

Posted
Posted

I know this is unlikely, but it is theoretically possible that you got two transmissions with the same internal problems. If you completely discount that as a possibility, then its possible that you may never find the problem.

  • Like 1
carkhz316 Enthusiast

carkhz316

Posted
Posted

Barring aftermarket electrical equipment (remote start, security, etc) malfunctioning, I'd put money on failing ignition switch. Very common problem on 99-02 trucks. There's even a TSB on it.

Motor City Rick Enthusiast

Motor City Rick

Posted
Posted

carkhz316,

 

TSB's are everything in a repair. Would save a lot of time and grief.

 

Can you list the TSB for PedroJ ?

carkhz316 Enthusiast

carkhz316

Posted
Posted (edited)

carkhz316,

 

TSB's are everything in a repair. Would save a lot of time and grief.

 

Can you list the TSB for PedroJ ?

Absolutely. I have experienced this myself when I was in Tech School. A friend brought his 99 Silverado 2500 (which I ended up owning some time later) to a local GM dealer. They couldn't figure it out. Told him BCM. Wrong. My instructor noted the TSB which the truck was showing the exact symptoms of. One new ignition switch later, and it was solved. I've since fixed this on a few other vehicles. Anyway, this is just a copy paste:

 

TSB# 01-07-30-002D

 

Malfunction Indicator Lamp On, Transmission Stuck in Second or Third Gear, Instrument Cluster Inoperative.

 

04-05 Rainier

99-00 Escalade

02-05 Escalade and EXT

03-05 ESV

97-99 Chevy/GMC Full Size; Pickup, Suburban, Tahoe (Yukon) (Old Style)

97-05 Blazer (Jimmy), (Bravada), Corvette, Express (Savana), S10 (Sanoma)

99-05 Silverado (Serria) (New Style)

00-05 Suburban, Tahoe, Yukon, Yukon XL

02-05 Avalanche, Trailblazer, EXT, Envoy, XL, XUV

04-05 Colorado/ Canyon

03-05 H2

04-05 GTO

With 4L60-E, 4L65-E, 4L80-E or 4L85-E

 

Condition: One or more of the following problems:

- The Malfunction Indicator Lamp is on.

- The transmission is defaulted to second gear (4L80/85-E).

- The transmission is defaulted to third gear (4L60/65-E).

- The instrument cluster is inoperative.

 

Possible DTC’s: P0720, P0753, P0758, P0785, P0787, P0973, P0976, P1860, P2761, P2764, and P2769 may be set depending on the vehicle.

 

Cause: The most likely cause of this condition may be a loss of voltage to the transmission on circuit 1020. This loss of power may be caused by an open in the ignition switch. This condition my also be the result of an incorrect installation of an aftermarket electronic device such as a remote starter or alarm system.

 

Correction: With the ignition switch in the RUN position, test for battery voltage at the appropriate fuse listed below.

97 S/T Trans 24

98-05 S/T Cluster 11

02-05 S/T Ignition 0

97-00 C/K(Old) Trans 20

99-05 C/K(New) Ignition 0

97-02 G-Van Trans 20

03-05 G, H-Van Ignition 0

03-05 H2 Ignition 0

04-05 GTO Auto Trans

97-04 Corvette Enging 1

05 Corvette ACC/TCM

04-05 Colorado/Canyon Trans

 

If the battery voltage is present at the fuse, inspect the ignition voltage circuit between the fuse and the transmission for possible opens. If the battery voltage is not present at the fuse, replace the ignition switch.

 

If the vehicle is equipped with an aftermarket electronic device and the DTC’s are being set when the device is being used, verify that the appropriate fuse listed above is being supplied battery voltage during operation. If voltage is not present at this fuse, these DTC’s will be set due to lack of voltage at the solenoids. This condition is most likely to occur with an incorrectly installed remote starting system. If this is the case, refer the customer to the installer of they system for corrections.

Edited by carkhz316
  • Like 1
PedroJ New Member

PedroJ

Posted
  • Author
Posted

Sorry it took me so long to reply I've been working on some other vehicles. Since I posted last I tried unplugging the pcm for an hour, and after I plugged it in in It went into a lower gear just for a while and I could manually shift from that to 3rd. Im not sure if it was 2nd or 1st. Also after I clear the codes and restart the engine, the codes are back before I even put it in gear. I pulled up the data display on the transmission and all three circuits say there open/short to ground. I also replaced the ignition switch and no luck. Another thing the cluster is working fine before and after the new ignition switch. I'm about to go over the harness from tranny to pcm. I also recently acquired a volt meter so I will be checking voltage on each wire. I think someone posted which ones to check and what to check for, but if not could someone point me in the right direction. Thanks to everyone for all the support. You are all great and amazing people.

Motor City Rick Enthusiast

Motor City Rick

Posted
Posted

Your next area will be the wiring / connectors "to" the transmission.

 

If there is "any" rust, corrosion, foreign material replace the pins (if you can), or replace the trans connectors as required. Look for broken / pulled out wires at connectors.

 

Disconnect then reconnect one transmission connector at a time to see if that changed anything.

  • Like 1
Motor City Rick Enthusiast

Motor City Rick

Posted
Posted (edited)

Stating that you changed 2 transmissions, ...and the problem is still there, .....tells me the problem is with the circuits leading to and from the transmission. Broken wire, poor electrical connection, backed out pin, blown fuse or a failed electrical component that is controlling the transmission.

 

Look at the commonality connection of all the problems, ....that will be your reference point of repair.

Edited by Motor City Rick
PedroJ New Member

PedroJ

Posted
  • Author
Posted (edited)

So I tested the E circuit wire at the transmission plug and it's only got 9.62 volts. Plus I inspected the wiring harness all the way from the tranny to the tcm no splits, breaks or exposed wired any where.

Edited by PedroJ
Motor City Rick Enthusiast

Motor City Rick

Posted
Posted

Go to" Ign0" fuse (10 amp). Measure the available voltage on both sides of that fuse. Is it the same as battery voltage? If yes, move on. If no, find high resistance back to the battery

 

Now disconnect the ECM (ignition off), to keep things simple, test all pink wires for battery voltage on the ECM connectors.

 

If any pink wire has no voltage, go check both sides of the fuses in the power distribution center (under the hood) and the fuse panel in the dash, check for blown fuse(s).

 

Now I need you to focus on checking for battery voltage with pin # 75 (pink wire on ECM connector), that feeds the "E" pin down by the transmission.

 

Is there battery voltage? If yes, that is good, now remove the trans connector with terminal "E" and measure for battery voltage to ground. Is there battery voltage?

 

If yes, available electrical power (battery voltage) is available to the transmission.

 

If no, high resistance issue back to "Ign0" fuse.

 

Check pin # 63 also (pink wire) on ECM connector. Is there battery voltage? If yes, move to terminal "E" on the trans connector with the trans connector disconnected. Measure voltage to ground, is there battery voltage???

 

If yes, available electrical power is available to the transmission.

If no, high resistance is in the circuit back to the power junction point.

  • 2 years later...
BattleCrymp New Member

BattleCrymp

Posted
Posted

Hey guys, I'm hunting the same issue.  Stuck in limp mode.  Have inspected entire harness from trans to PMC.  One thing that sticks out is two pink wires going to trans 1 has good voltage with test light 2 has lower voltage (light is much dimmer).  When I turn ignition on one wire loses power completely.  So the question is should both stay hot or not?  Can I send temp power to the dead wire to see if it come out of limp mode?  05' silverado 5.3 4x4 4L60e.  Thanks in advance.

  • 4 months later...
Duggie New Member

Duggie

Posted
Posted

I have an ‘04 trailblazer Ext with the PO785 code but when I clear the code with my OBD11 tester it works ok until I drive for a while then it comes back when I get to about 35 mph 

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