Info - Component Slipping/DTC P1870 - Diagnosis. GMC Truck Yukon

Subject:

Component Slipping/DTC P1870 - Diagnosis

Models:

1996 Buick Roadmaster

1996 Cadillac Fleetwood

1999 Cadillac Escalade

1996-99 Chevrolet Camaro, Corvette

1996-99 Pontiac Firebird

1996-99 Chevrolet and GMC C/K, M/L, S/T, G Models

1996-99 Oldsmobile Bravada

1996-99 Holden Commodore

with Hydra-matic 4L60-E (RPO M30)

Description

Many technicians experience difficulty when diagnosing 1996-1999 4L60-E transmissions with a DTC P1870 (Transmission Component Slipping).

The purpose of this bulletin is to provide assistance for technicians that have already completed the DTC P1870 diagnostic table in the Service Manual. This bulletin will provide a diagnostic strategy for solving DTC P1870 concerns as well as give some of the most common causes for a DTC P1870.

General Information

Important:

•	Chevrolet Camaro, Pontiac Firebird with 3.8L V6 Engine experiencing a slip condition at 70-90 km/h (45-55 mph) when the TCC applies should refer to Corporate Service Bulletin 77-71-70A for calibration re-flash.

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1996 Chevrolet and GMC C/K, M/L, S/T, G Models, and 1996 Oldsmobile Bravada with VCM and 4L60-E (RPO M30) with a slip or flare on the 1-2 and/or 2-3 upshift, or no 3rd or 4th gear, or launch shudder should refer to Corporate Service Bulletin 66-71-03A to ensure that a poor internal ground in the VCM does not exist.

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A DTC P1870 indicates that a mechanical malfunction exists. If any other DTC's set along with a DTC P1870, then diagnose those first. A DTC P1860 (TCC PWM Solenoid Circuit Electrical) will set if a TCC PWM solenoid circuit failure exists. A DTC P0740 (TCC Enable Solenoid Circuit Electrical) will set if a TCC enable solenoid circuit failure exists.

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When attempting to duplicate DTC P1870, it is critical that a normal operating temperature of 82°C (180°F) to 93°C (200°F) be reached. It may be difficult to attain the transmission temperature required to adequately cause the DTC to duplicate. Allow the vehicle to idle to assist in warming the powertrain.

•	Optimum speed to duplicate the DTC P1870 is between 89 km/h (55 mph) and 107 km/h (63 mph).

•	Commanding the TCC ON and OFF several times with the Tech II is critical to monitoring slip when sticky valves in the valve body are suspect.

•	If the customer brought in the vehicle for a temporary harsh 1-2 shift and no driveability concerns are seen during a test drive, then remember that a harsh 1-2 is a result of the PCM commanding maximum line pressure from recognizing a DTC P1870.

•	The PCM must recognize that a DTC P1870 has set in two consecutive key cycles to illuminate the MIL. If a DTC P1870 is not recognized on a second key cycle, then normal line pressure returns.

•	Vehicles should be inspected for correct tire size, axle ratio, or calibration.

Diagnostic Approach

Action	Yes	No
Attempt to duplicate DTC P1870. Did you duplicate DTC P1870?	Go to Slip Check Procedure	Go to TCC System Symptom Table

Action

Yes

Attempt to duplicate DTC P1870.

Did you duplicate DTC P1870?

Go to Slip Check Procedure

Go to TCC System Symptom Table

Slip Check Procedure

This procedure will assist in isolating what area of the transmission is causing your slip, either the TCC system or internal transmission components. After you have isolated the origin of the slip, then utilize the TCC System Symptom Table or the Internal Transmission Symptom Table of this bulletin for most common concerns.

To check for a TCC system concern

TCC slip can occur either hot or cold or in both conditions. First, perform the following test at cold transmission temperatures, then perform the same test at normal operating temperature. Ideal slip from the transmission with the TCC applied is 50 RPM or less under light to normal throttle, no heavy engine load or hard accelerating conditions.

Use the Tech II scan tool to monitor TCC slip while driving the vehicle in 4th gear at steady speed with the TCC commanded ON.
When the TCC is applied or released (release the TCC with brake pedal, not the scan tool - release the TCC by lightly applying the brake pedal while simultaneously maintaining a steady throttle position), the slip speed should drop or rise 150-300 RPM. If the slip speed does not drop, then the DTC P1870 is being caused by the torque converter system.

Action	Yes	No
Did TCC slip speed drop (150-300)?	Continue Slip Check Procedure for an internal trans concern	Go to TCC System Symptom Table

To check for an internal transmission concern

Slip should be checked in every gear to isolate in which gear the slip may be occurring. Drive the vehicle in each forward gear range D1, D2, D3 and D4. Command the TCC ON with the Tech II in each gear and monitor slip speed.

Important: Vehicle speed must be over 11 km/h (7 mph). Some TCC slip is normal when the TCC applies directly after 11 km/h (7 mph) is reached.

If the slip speed remains constant from gear to gear, then the condition is most likely TCC related. Example: Slip speed is higher in second and fourth gear than in third gear. This would lead a technician to a possible slipping band.

Action	Yes	No
Is slip speed equal in all gears?	Go to TCC System Symptom Table	Go to Internal Transmission Symptom Table

Important: These symptom tables are to be used when the following symptoms are associated with a DTC P1870.

TCC System Symptom Table

Symptom

Causes

TCC SLIP (100 RPM SLIP)

•	Check for bronze bushing material in the pan and filter. If bronze material is present, then the stator bushings (234) and turbine shaft (241) should be replaced (Bronze bushing may turn black with an acrid odor).

•	The turbine shaft and housing (621) should be replaced if damaged.

•	In rare instances, it may be necessary to check for an overheated torque converter (24) (Blue and/or distorted converter).

•	TCC solenoid (66) - Perform leak check.

•	Converter clutch valve (224) in pump should be checked for 13 mm (0.500 in) of bore travel without binding.

•	Turbine shaft O-ring seal (618) cut.

•	Turbine shaft hole not drilled to full depth. This concern can be checked by squirting trans fluid through the turbine shaft hole to check for full flow. This is a low mileage failure.

NO TCC APPLY (300 RPM SLIP)

•	Converter clutch valve (224) stuck closed (Check for debris in valve bore).

•	TCC PWM solenoid (396) broken/cracked. Visually inspect solenoid.

•	TCC solenoid (66). Perform leak test.

•	Turbine shaft O-ring seal (618) omitted.

TCC SLIP WITH STALL STUMBLE

Converter clutch valve (224) stuck open (TCC is applying).

INTERMITTENT TCC, OK COLD, SLIPS HOT

•	TCC PWM solenoid (396). Leak test solenoid.

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The TCC regulator apply valve (380) and/or converter clutch shift valve (224) may be sticking/side-loading. It is possible there will not be any damage to the valve upon inspection. Transmissions produced after 2/1/98 will have a groove cut into the spring end of the regulator apply valve. This design is to help float the valve in its bore (replace valve body assembly).

Internal Transmission Symptom Table

Symptom

Causes

3RD OR 4TH GEAR SLIP

•	3-2 downshift solenoid (394) ball seat retention failed. Leak test solenoid. Usually associated with a 3-4 clutch/band worn.

•	3rd accumulator retainer and ball assembly (40) leaks. Test for proper check ball operation. Usually associated with burned 3-4 clutch.

NO 4TH OR SLIPPING 4TH

•	Check ball in the wrong location or extra check ball that has dropped behind the spacer plate during trans assembly. The extra check ball can block the 4th apply servo feed.

•	Clutch orifice cup plug (238) not fully pressed in.

SLIP/FLARE IN ANY GEAR

Pump slide inner spring (207) or outer spring (206) omitted causing a slow slide response.

NO 3RD

Clutch orifice cup plug (238) blown out.

HARSH 1-2 UPSHIFT

4-3 sequence valve (383) stuck in bore by sediment.

NO 2-3 UPSHIFT

2-3 shift valve (368) or 2-3 shuttle valve (369) stuck in bore by sediment.

NO 3-4 UPSHIFT

3-4 shift valve (385) stuck in bore by sediment.

Service Information

Refer to the appropriate Service Manual for replacement procedures.

Warranty Information

Labor Code: Refer to Labor Time Guide for correct labor operation. Please use the closest available labor operation for the diagnosis performed.