4t65e code p1811

22 GEARS June/July 2002

C omplaints of harsh upshifts inthe 4T65E transaxle, withDTC P1811 and possibly ashudder on acceleration, are frequentlysymptoms of an underlying line pres-sure control problem. In this article,were going to take a look at the causesfor these conditions, focusing on under-standing and diagnosing the pressurecontrol system.

While the 4T65E transaxle is verysimilar to the 4T60E, pressure controlis one major system that sets these twounits apart. Instead of a vacuum modu-lator, the 4T65E uses a PCM(Powertrain Control Module) con-trolled Pressure Control SolenoidValve, for line pressure control. Thissystem enables the PCM to control shiftfeel, and adapt to different driving con-ditions, engine load, and variations inmanufacturing tolerances and transaxlewear.

Electronic pressure control also

means the PCM can control the feel ofengagements, and adjust line pressureduring steady state operation to com-pensate for engine load changes. ThePCM can even raise line pressure if itdetects a slip, and store that adjustmentin memory. This allows the system tokeep line pressure to a minimum, sopower isnt wasted by the pump havingto maintain unnecessary pressure. Thisincreases the overall powertrain effi-ciency.

A Pressure Control Solenoid Valveand three other valve lineups worktogether to control line pressure rise.

The PCM controls the solenoid bysending a variable duty cycle signal tothe high (positive) side of the solenoidat a fixed frequency of 292.5 Hz. ThePCM also provides the low (negative),or ground path (figure 1). The dutycycle percentage, or signal on-time, isused to control the current through thesolenoid. A higher duty cycle percentage

by Mike Van Dyke

4T65E HEADACHEST h e C a u s e s f o r, a n d

D i a g n o s i s o f , C o d e P 1 8 1 1

The PCM doesntlight the Malfunc-

tion IndicatorLamp when P1811sets, so the onlysymptoms youmight have areharsh engage-

ments andupshifts.

Figure 1 Figure 2

Case Cover

Actuator FeedLimit Valve

MIKEVD4T65E.qxd 5/30/02 3:38 PM Page 22

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causes increased current through thesolenoid, and a lower percentage causesdecreased current. The PCM monitorsthe current and adjusts the duty cycle tomaintain the desired average current.

The Pressure Control SolenoidValve operates on the feed/bleed princi-ple. The valve is fed a regulated supply

of actuator feed oil from the ActuatorFeed Limit Valve, located in the chan-nel plate (figure 2). The Actuator FeedLimit Valve limits oil pressure feedingthe solenoid to a maximum of about115 PSI to prevent solenoid flooding;that is, to keep it from being fed moreoil than its designed to exhaust.

Actuator Feed oil is fed through a0.035 orifice, located underneath thescreen, in the snout of the PressureControl Solenoid Valve (figure 3).Magnetic force from the currentthrough the solenoid windings acts onthe plunger, which controls how muchforce is applied to the Pintle Valve. Thiscontrols the solenoids rate of exhaust,or bleed, and creates a variable boostsignal (VBS), which controls the posi-tion of the Torque Signal RegulatorValve, located in the valve body behindthe Pressure Control Solenoid Valve

4T65E Headaches

Figure 3Trapped


GEARS June/July 2002 25

(figure 4).The Torque Signal Regulator Valve

takes line pressure and modulates itdown to boost pressure, called TorqueSignal Pressure (equivalent to EPCpressure in a Ford). Torque SignalPressure is then fed to the Line BoostValve, located in the pressure regulator

valve lineup.The Line Boost Valve acts directly

on the Pressure Regulator Valve toboost line pressure. The PressureRegulator Valve function is the same asthat of a 4T60E, or a 700R4, for thatmatter. It controls the amount ofdecrease pressure sent to the pump,

depending on the line pressure demand.Decrease pressure reduces pump outputby forcing the pump slide back againstthe pump slide spring, which lowerspump displacement. If the pump slide isalready at minimum displacement, thenthe Pressure Regulator Valve will beginto exhaust line pressure.

Figure 4

Discard this clip

Torque SignalRegulator Valve

Pressure ControlSolenoid Valve

Any pressure

readings that

deviate from this

chart indicate a

line pressure con-

trol problem.

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Looking at figure 5: The Actuator Feed Limit

Valve limits the feed pressureto the Pressure ControlSolenoid Valve.

The Pressure ControlSolenoid Valve controls thepressure to the Torque SignalRegulator Valve.

The Torque Signal RegulatorValve controls the pressure tothe Line Boost Valve.

The Line Boost Valve pusheson the Pressure RegulatorValve to increase line pres-sure.

Got all that? Its a little more com-plicated than say, a 4L60E, but theresreally only one more valve added to thesystem: the Torque Signal RegulatorValve.

GM uses an adaptive learn strategyfor the 4T65E control system. In thissystem, the PCM analyzes the time ittakes to complete each shift, comparesthat to a desired time, then stores avalue to adjust line pressure for the nexttime the shift occurs under the sameengine load conditions.

These are all calculated pressures;the PCM has no way of monitoring theactual line pressure. The PCM is pro-grammed with a baseline pressure risecurve, and these adjustments representline pressure that is added to, or sub-tracted from, the base curve. These linepressure adjustment values are stored inwhat are called TAP cells. TAP standsfor Transaxle Adaptive Pressure; a cellis just a fancy name for a memory loca-tion.

Transmission operation is brokendown into states, such as 1st gearsteady state, which is cruising or accel-erating in 1st gear, or 1-2 shift, which isthe state of operation when the 1-2 shiftis commanded. For each transmissionstate, there are TAP cells numberedfrom 4 to 16, which the PCM can referto. Each successive TAP cell representsan increase of 12.5 ft-lbs of calculatedengine torque output. In other words,when you accelerate hard, the PCMrefers to the higher numbered TAP cells(13-16); under moderate acceleration,the PCM refers to the lower numberedTAP cells (4-6). TAP cells can beviewed in scan tool data (figure 6).

DTC P1811 (maximum adapt andlong shift) sets when the PCM reachesthe maximum adaptive limit of pressurerise that it can command to complete anupshift within a desired time. P1811 isset on the 2nd occurrence of a long shiftduring one ignition cycle. A long shift isdefined as an upshift that is 0.65 sec-

onds longer than the desired time.When the code sets, the PCM com-mands maximum line pressure and dis-ables shift adapts. The PCM doesntlight the Malfunction Indicator Lampwhen P1811 sets, so the only symptomsyou might have are harsh engagementsand upshifts.

The most common causes for DTCP1811 are:

Pressure control solenoid fail-ure

Sediment, debris, or wear inthe valve body, causing thetorque signal regulator valve tostick or not function properly

Sediment debris, or wear invalve body, causing the actua-tor feed limit valve to stick ornot function properly

Line boost valve and sleeveassembly worn or sticking

PCM calibration

Use the following steps to aid inyour diagnosis:

1. Make sure the vehicle has thelatest calibration (software,firmware, etc.) installed. 1998Buick LeSabre and ParkAvenue, Oldsmobile EightyEight, and Pontiac Bonnevillewith 3.8L V6 engines (8th VINcharacter K) have a PCM cali-bration update to address aninsufficient line rise command,which can cause a shudder or


Figure 6

4T65E Headaches

Figure 5


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slip during hard throttle accel-eration, after slowing down fora stop. The chart in figure 7lists the original calibrationnumbers with their respectiveupdates. Check your vehiclescalibration number with a scantool to verify whether calibra-tion update is needed.

2. Perform a line pressure test:Connecting a 0-300 PSI gaugeto the line pressure port, anduse a scan tool to control linepressure. Compare the read-ings to the chart in figure 8.

Keep in mind, the scan toolwill only control line pressurein park and neutral.

Any pressure readings that deviatefrom this chart indicate a line pressurecontrol problem. Without disassem-bling and inspecting the unit, theres noway to tell for sure what the cause of thefailure is. Heres some information tohelp you decide how to approach therepair:

1. 4T65E pressure control sole-noids have a high failure rate,even at relatively low mileage.If the trans is clean and free

from debris, and the vehiclehas relatively low mileage (lessthan 50,000 miles), the pres-sure control solenoid is veryoften the cause of the problem.A bad pressure control sole-noid can exhibit poor line pres-sure control in just one area,sometimes in the 80-to-120PSI range, but work fine in allother areas. Or it can functionproperly at lower pressure, butnot give enough line rise whenhigher pressures are command-ed, causing a slip or shudderunder hard acceleration.

2. If the vehicle has considerablemileage (more than 50,000miles) or theres debris in thepan or filter, look for worn orsticking valves. Pay particularattention to the Torque SignalRegulator Valve and bore (fig-ure 4), the Actuator Feed LimitValve and bore (figure 2), andthe Line Boost Valve andsleeve assembly (figure 9).

Until next time, remember: Whiletransmissions and control systems havebecome more complicated, the simplestand most often overlooked tests canoften save you valuable diagnostic time.Even in this high-tech world of elec-tronics and computers, sometimes youjust have to put a gauge on it!


Pressure Control ApproximateSolenoid Valve Line Pressure

Current 0 amp 243-310 psi0.1 amp 241-308 psi0.2 amp 234-305 psi0.3 amp 225-300 psi0.4 amp 210-288 psi0.5 amp 190-276 psi0.6 amp 170-254 psi0.7 amp 145-222 psi0.8 amp 115-178 psi0.9 amp 82-130 psi1.0 amp 68-93 psi1.1 amp 65-80 psi

Original Calibration New CalibrationFile Number File Number09361284 0937977409361294 0937978409360304 0937979409361314 0937980409361324 0937981409361334 0937982409361344 0937983409361354 0937984409361364 0937985409361374 0937986409361384 09379874

1998 Calibration Updates

4T65E Headaches

Figure 7 Figure 8

Figure 9

PressureRegulator Valve

Inspect for wear, scoring,or excessive clearance

Reverse Boost Valve

Line Boost Valve


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4t65e code p1811

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