AW 6 Speeds: Valve Body Diagnosis

One of the focal points for diagnostics should be monitoring C- 2/N282 and C-3/N90 solenoid activity. Common complaints with this valve body include 2-3 flare, loss of or slip on 3-4, and harsh coast 5-3 or 4-3 downshifts. Each linear solenoid reacts on a clutch-control valve, which then affects clutch application and release. Having one solenoid for each clutch allows for "skip-shift" upshifts and downshifts. Without a scan tool or pressure gauge, identifying which solenoid, clutch or clutch control valve is being activated becomes very difficult.

As the torque-converter clutch generally applies after the 2-3 shifts, TCC application can easily be confused with a 3-4 shift. The TCM modulates TCC slip or releases the converter briefly during upshifts and downshifts. The TCM can use lockup to control engine braking in certain applications.

Test Drive

To begin, you will need the powerflow chart to help identify which solenoid or clutch valve requires acattention. A scan tool with graphing capability is the second of three requirements for that drive. The third requirement is unusual: If possible, have the vehicle owner drive and duplicate the concern, or at least provide a detailed description of how to duplicate the problem. Because this is a six-speed with skip-shift capability and a modulated converter clutch, duplicating and isolating the driver's complaint can be very difficult. Operator driving habits, TCM adaptability and terrain will all greatly affect the shift strategy. I would suggest graphing in real time, monitoring engine speed and turbine speed. When shift quality is smooth and correct, turbine speed will parallel engine speed. With a flare/neutral condition, the engine speed spikes up. With a bind or bumpy shift caused by an overlap issue, the turbine speed will dip at the beginning of the shift. Generally one shift will have the problem, so you could compare a good rpm ramp with a poor rpm ramp.

Comparing two rpm inputs will identify each shift, as well as TCC full application/zero slip or partial modulation. The test drive should identify the complaint as being related to a specific clutch or to all shifts. If only one clutch is involved, focus on the linear solenoid and clutch-control valve that exhaust and charge that clutch. The AW6 input-speed graph (Figure 4) shows engine speed in red and turbine speed in green. Two shifts have been captured in this graph, showing a compatible ramping of the two signals throughout.

Pressure Testing

Figure 5 shows typical C-1 clutch pressure. With harsh upshifts and downshifts, it is common to have elevated line pressure, which can be caused by a worn main pressure-regulator bore or PCA solenoid. To isolate this, tap into C/K-1 pressure, clear the codes and monitor N93/PCA amperage. With elevated line pressure, engagements become harsh and downshifts bumpy, and the 2- 3 develops a flare under light acceleration. Elevated line pressure may not set or be caused by codes. With the complaint of harsh shifts from 3 to 6 and 6 to 3, and C/K-1 pressure has not been elevated, you should tap TCC release (Figure 6). As mentioned, the TCM strategy brings the converter clutch on directly after the 2-3 shift. It will go to full application at light load. If you are graphing engine and turbine speed, lines should be overlaid at full application. TCC will be modulated off to disconnect the turbine shaft during subsequent upshifts and downshifts. If this control is not evident on your graph and release-presceleration. Elevated line pressure may not set or be caused by codes. With the complaint of harsh shifts from 3 to 6 and 6 to 3, and C/K-1 pressure has not been elevated, you should tap TCC release (Figure 6). As mentioned, the TCM strategy brings the converter clutch on directly after the 2-3 shift. It will go to full application at light load. If you are graphing engine and turbine speed, lines should be overlaid at full application. TCC will be modulated off to disconnect the turbine shaft during subsequent upshifts and downshifts. If this control is not evident on your graph and release-pressure test, inspect the TCC control bore for wear. The scan tool will indicate an amperage change, but the TCC release pressure will not be affected (Figure 7). If the vehicle is driven in this condition for too long, the converter lining can be damaged.

Clutch-Circuit Testing

Transmission circuits can be tested in the vehicle as explained earlier or with the valve body removed. For a wet air test (WAT), prime the circuit with ATF, then follow by applying 40-60 psi of air. The familiar "dull thud" of a piston stroke confirms a good circuit. During the WAT, if the pressure drops and the clutch does not apply, or vents, you have identified a leak. On the 09G, for example, if the K-2 piston does not stroke or fluid exhausts from another port, the K-2 case sleeve may have rotated.

Valve-Body Inspection

If you determine that the valve body is at fault, or you are inspecting a valvebody core for future use, inspect the bores mentioned previously. Exploded view, vacuum testing locations for each bore, and relief and spring identification are available in the tech resources section of the Sonnax website.

As mentioned, the TCC control tends to wear first, then solenoid modulators, followed by K-2/K-3 clutch control and then main or secondary regulator valves. If your test drive indicated a harsh shift in one gear and line pressure is good, focus on the specific clutch-control valve identified in the power-flow chart. Bore wear in this type of valve body is similar in appearance to that found in AW 55-50 or other units. Wear appears as a polished half-moon area, typically on the loaded side of the bore and at the ends of the valve travel. The valves themselves rarely have witness marks or evidence of a problem.

Diagnosis and the Pileated Problem

At this point you should realize that this transmission offers a large window of opportunity. The fact is that paper can help you isolate a problem in the AW 6; being hasty in your evaluation could cost money by unnecessary transmission removal and misdiagnosis. For those of us with a pileated woodpecker breaking windows, we should remember the following:

Cover the windows with paper for at least two weeks, allowing time for the birds to find another territory. Taking the paper down too early will result in the woodpecker coming back to finish the job. This results in time and money to repair damage.