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Discussion Starter #1
Just installed new torque converter and transgo jr. Shifter will go through all the gears fine no binding. Indicator light will not come out of park and will turn on and off every few seconds or so. Truck will give a slight jolt if it’s in drive position when the light comes back on. Any help is appreciated. Thanks
 

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Just installed new torque converter and transgo jr. Shifter will go through all the gears fine no binding. Indicator light will not come out of park and will turn on and off every few seconds or so. Truck will give a slight jolt if it’s in drive position when the light comes back on. Any help is appreciated. Thanks
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Please take a moment to tell us more about the truck( ie. Year, Make, and Model, etc..) and list any known mods done.
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Discussion Starter #3
Truck is a 2007 classic LBZ. Truck mods are intake, full exhaust from manifolds to straight pipe. Dmaxstore torque converter and transgo jr. Located down in southern Utah
 
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You have missed the shift pin in the shift valve--or the wrong place—
Take the pan back off, get the shift pin back in the valve body correct. Simple fix. Good luck.
There’s lots of YouTube videos and directions on this.
 

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Discussion Starter #5
The shift pin is in where it needs to be in the shifting mechanism. As far as I can tell there’s only one way it goes in. The shifter moves freely and I can still select neutral and park
 

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Discussion Starter #6
Throwing codes p0852, p0843, p0877
 

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Codes p0852, p0843, p0877
These three code are leading to your IMS Switch.
GM Part :29546972 SWITCH, Transmission Oil Pressure, SWITCH,TRANS FLUID PRESSURE(INCLUDES TEMPERATURE SENSOR) Replaced by:24293418

Your IMS could have gotten dirt, o-ring, bolts not torqued right, not plugged in correctly, etc.
You need to go over your transgo jr. installation.
https://www.dieselplace.com/forum/71-information-place/19-do-yourself-useful-articles-product-reviews/122621-transgo-jr-install-step-step-pics-included-best-i-could-do.html

P0852
Circuit/System Description

The engine control module (ECM) provides 12 volts to the park/neutral position (PNP) switch. The switch consists of 5 separate circuits, 4 of which indicate gear selector position to the transmission control module (TCM), and one that indicates park/neutral position to the ECM. When the transmission is in Park or Neutral, the switch closes and pulls the ECM voltage low, 0 volts. When the transmission is not in Park or Neutral, the ECM voltage is high, 12 volts. The ECM uses the switch in order to enable starter operation.

Conditions for Running the DTC

DTC P0851
Ignition voltage is between 11-18 volts.
The ignition is ON.
DTC P0852 is not active.
DTC P0852

Ignition voltage is between 11-18 volts.
Ignition is ON.
DTC P0851 is not active.
No GMLAN error messages.
Engine speed is more than 650 RPM.
Actual engine torque is more than 120 N.m (89 lb ft).
Accelerator pedal position is more than 6 percent.
Vehicle speed is more than 24 km/h (15 mph).
Conditions for Setting the DTC

DTC P0851

The ECM detects the Park/Neutral switch signal equals 12 volts (high) when the IMS reports a Park/Neutral range for 5 seconds.

DTC P0852

The ECM detects the Park/Neutral switch signal equals 0 volts (low) when the IMS reports a Drive range for 5 seconds and the following conditions are present:


TP is equal to or greater than 6 percent.
Engine torque is equal to or greater than 120 N.m (89 lb ft).
Vehicle speed is equal or greater than 24 km/h (15 mph).
Action Taken When the DTC Sets


DTCs P0851 and P0852 are Type C DTCs.
The ECM uses IMS range for engine start-up.
Conditions for Clearing the DIC/DTC

DTCs P0851 and P0852 are Type C DTCs.

Diagnostic Aids

It is possible for this DTC to set due to a stack-up or misalignment issue between the IMS and the P/N Switch, where no electrical fault is present. Ensure the gear shift selector cable is properly adjusted and there are no service bulletins that address this concern before replacing parts.

Circuit/System Verification

If there are any other engine or transmission related DTCs set, diagnose those DTCs first. With a scan tool observe the Park/Neutral switch parameter in the engine controls data list and move the gear shift lever from Park, to Reverse and through all the ranges and observe the parameter as you move the shift lever. The parameter should display Park/Neutral when in Park or Neutral and In-Gear when in Reverse, Drive or Drive Low. It is especially important to closely observe the Park and Neutral to Drive transitional positions while moving the shift lever and observing for possible misalignment or slack in the shifter mechanism.

Circuit/System Testing


Ignition OFF, transmission in Park or Neutral, disconnect the transmission 20-way connector.
Test for less than 1 ohm of resistance between the Park/Neutral signal circuit terminal R on the transmission side and ground.
¤ If greater than the specified range, test the signal circuit between the connector and the IMS for an open/high resistance. If the circuit tests normal, replace the IMS.
Ignition On, verify the Park/Neutral parameter displays In-gear.
¤ If not the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM.
Install a fused jumper between the signal circuit and ground. Verify the Park/Neutral parameter displays Park/Neutral.
¤ If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
1) ECM replacement. Refer to Control Module References for replacement, setup, and programming.
2) IMS replacement. Refer to Manual Shift Shaft, Detent Lever, and Position Switch Assembly Replacement

P0843 = Transmission Fluid Pressure Sensor/Switch "A" Circuit High
The TFP switches may stick from time to time causing a code to set.

P0877 Transmission Fluid Pressure Sensor/Switch “D” Circuit Low
 

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Discussion Starter #8
When I removed the ims from the valve body I did not see any o rings. I assumed that they were stuck to the underside of them or something. I’ll drop the pan and check for them. If they are missing, should they be replaced with any certain kind?
 

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Discussion Starter #9
So I’ve double and triple checked my valve body and all seems to be in order. The blue ims has all of its o-rings, dirt free and all plugged in correctly. It all worked fine before so I’m still led to believe I’ve done something wrong somewhere. I believe the harness was pinched a little when I put the trans mount in, but upon inspection I don’t see any damaged wires on the harness. Could this have shorted anything? Could the ims just have gone bad? I read the instructions posted above but to be honest this is my first auto trans/electrical problem and quite a newbie at this
Thanks
 
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