P1870 Explained

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P1870 Explained

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P1870 Explained - 3/10/2008 9:00:05 PM

swartlkk

Posts: 14530
Joined: 5/1/2005
From: Waterloo, NY
Status: offline

P1870

Schematic

CIRCUIT DESCRIPTION
The Vehicle Control Module (VCM) monitors the difference between engine speed and transmission output speed. In D3 drive range with the TCC engaged, the engine speed should closely match the transmission output speed. In D4 drive range, with the TCC engaged, the TCC slip speed should be -20 to +50 RPM .

When the VCM detects excessive TCC slip when the TCC should be engaged, then DTC P1870 sets. DTC P1870 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC

* No TP sensor DTCs P0122 or P0123.
* No VSS assembly DTCs P0502 or P0503.
* No TFT sensor DTCs P0711, P0712 or P0713.
* No TCC solenoid valve DTC P0740.
* No 1-2 SS valve DTC P0753.
* No 2-3 SS valve DTC P0758.
* No TFP manual valve position switch DTC P1810.
* No TCC PWM solenoid valve DTC P1860.
* The engine speed is greater than 450 RPM for 5 seconds .
* The engine is not in fuel cutoff.
* The engine torque is 50-400 lb ft .
* The engine vacuum is 0-150 kPa .
* The TP angle is 9-35% .
* The vehicle speed is 48-112 km/h (30-70 mph ).
* The engine speed is 1500-3000 RPM .
* The speed ratio is 0.69-0.88 (speed ratio is engine speed divided by the output speed).
* The gear range is D4.
* The commanded gear is not 1st gear.
* The TFT is 20-130°C (68-266°F) .
* The shift solenoid performance diagnostic counters are zero.

CONDITIONS FOR SETTING THE DTC
DTC P1870 sets if the following conditions occur for three TCC cycles.

* The TCC is commanded ON for 5 seconds .
* The TCC is at maximum duty cycle (95% ) for 5 seconds .
* The TCC slip speed is 130-800 RPM for 7 seconds .

ACTION TAKEN WHEN THE DTC SETS

* The VCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
* The VCM commands maximum line pressure. The VCM inhibits TCC engagement. The VCM inhibits 4th gear if the transmission is in hot mode.
* The VCM freezes shift adapts from being updated.
* The VCM records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Freeze Frame and Failure Records.
* The VCM stores DTC P1870 in VCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.

CONDITIONS FOR CLEARING THE MIL/DTC

* The VCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
* A scan tool can clear the MIL/DTC.
* The VCM clears the DTC from VCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
* The VCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the VCM.

DIAGNOSTIC AIDS

* Bronze material found in the transmission oil pan may indicate stator shaft bushing wear. If bushing wear is suspected, inspect the stator shaft and the input (turbine) shaft for damage.
* Refer to Symptom Diagnosis for more information.

Diagnostic Chart (Part 1 Of 4)

Diagnostic Chart (Part 2 Of 4)

Diagnostic Chart (Part 3 Of 4)

Diagnostic Chart (Part 4 Of 4)

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.

3. This step tests the torque converter for slippage while in a commanded lock-up state.

< Message edited by swartlkk -- 7/2/2008 6:17:44 PM >

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04 Rainier
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Post #: 1

RE: P1870 Explained - 3/10/2008 9:05:31 PM

swartlkk

Posts: 14530
Joined: 5/1/2005
From: Waterloo, NY
Status: offline

Also worth noting is a TSB which I posted:

quote:

ORIGINAL: swartlkk

Here''s all of the information:

quote:

A/T - 4L60-E Harsh 1-2 Gear Upshift/MIL/SES/CEL ON

File In Section: 07 - Transmission/Transaxle

Bulletin No.: 01-07-30-023B

Date: March, 2002

TECHNICAL
Subject:
Harsh 1-2 Upshift, SES, MIL, or CEL Illuminated, DTC P1870 Set
(Replace Valve Body)

Models:
1996 Buick Roadmaster
1996 Cadillac Fleetwood
1999-2000 Cadillac Escalade
1996-2000 Chevrolet Camaro, Corvette
1996-2000 Pontiac Firebird
1996-2000 Chevrolet and GMC Light Duty Truck Models
1996-2000 Oldsmobile Bravada
with 4L60-E Automatic Transmission (RPO M30)
Built Prior to January 15, 2000 (Julian Date 0015)

This bulletin is being revised to update VIN Breakpoint Date information and revise the Parts Information table. Please discard Corporate Bulletin Number 01-07-30-023A (Section 07 - Transmission/Transaxle).

Condition

Some customers may comment on a harsh 1-2 upshift and the Check Engine Light or Service Engine Soon indicator is illuminated.

Diagnosis

Typically, these vehicles will have been driven more than 32,000 km (20,000 mi) before this condition occurs.

The scan tool may show a DTC P1870 set as a history code.

A harsh 1-2 shift or DTC P1870, caused by wear in the control valve body, may be difficult to duplicate when the transmission temperature is below 93°C (200°F).

Cause

The condition may be due to wear in the control valve body. This wear occurs in the bore that contains the TCC isolator and regulator valves, and results in poor, or no, TCC apply.

Important :
^     DTC P1870 is a type B code. The conditions for setting the P1870 DTC must occur on TWO CONSECUTIVE TRIPS (ignition cycles, with a drive cycle) before setting a P1870 history code.
^     When the conditions for setting DTC P1870 are met (first trip), the PCM commands maximum line pressure and harsh 1-2 shifts are the result.
^     This may result in a harsh 1-2 shift with no history code if the conditions for setting the DTC required for the second trip are not met, on two consecutive trips (Ignition cycles, with a drive cycle).
^     When the conditions for setting the DTC are met, on the second consecutive trip, a DTC P1870 is stored as a history code.
^     When the P1870 code is stored, the PCM will turn on the Service Engine Soon (SES), Check Engine Light (CEL), or Malfunction Indicator Lamp (MIL).

Correction

Install a control valve body with the revised TCC regulator and isolator valves. Refer to the Parts Information table below. These valves are used in all transmissions produced after January 15, 2000 (Julian Date 0015), and all of the service parts currently available through GMSPO contain revised TCC regulator and isolator valves.

Important : If all of the following conditions are true, it is not necessary to rebuild the transmission or to replace additional transmission components beyond the control valve body.
^     Transmission operation is normal before the transmission reaches operating temperature, or before DTC P1870 is set (no slips, flares, or missing gears).
^     The torque converter is not blue or overheated.
^     The transmission fluid is not burned or has no burned odor
^     The transmission fluid pan contains no abnormal debris (clutch material, bronze, brass, or metal fragments).