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Which Came First, the Chicken or the Egg?

Codes setting codes is not a new concept in the automotive industry. An example of this in the world of transmissions occurs in Dodge vehicles using the 41TE transaxle. If it develops a gear-ratio-error code such as P0731/2/3/4, code 1790 “Fault Immediately After Shift” can also be present as a result of the gear-ratio code or codes. In fact, the explanation given by the manufacturer for setting this code is: This code is set if the associated speed ratio code is stored within 1.3 seconds after a shift.

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Which Came First, the Chicken or the Egg?

Shift Pointers

Subject: Codes set as a result of other codes
Units: 41TE, B7WA
Vehicle Applications: Dodge; 2003 Acura 3.2TL
Essential Reading: Rebuilder, Diagnostician
Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

Shift Pointers

  • Subject: Codes set as a result of other codes
  • Units: 41TE, B7WA
  • Vehicle Applications: Dodge; 2003 Acura 3.2TL
  • Essential Reading: Rebuilder, Diagnostician
  • Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

Codes setting codes is not a new concept in the automotive industry. An example of this in the world of transmissions occurs in Dodge vehicles using the 41TE transaxle. If it develops a gear-ratio-error code such as P0731/2/3/4, code 1790 “Fault Immediately After Shift” can also be present as a result of the gear-ratio code or codes. In fact, the explanation given by the manufacturer for setting this code is: This code is set if the associated speed ratio code is stored within 1.3 seconds after a shift.

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Back in the day when gear-ratio codes for these vehicles were 50, 51, 52, 53 and 54, code 36 was the “Fault Immediately After Shift” code. The theory of operation for this code provided by the manufacturer back then read: This code will only be stored along with a 50 series code. If this code is set, it indicates the problem is mechanical in nature. When this code exists, diagnosing the transmission should be based on the associated speed ratio code and only mechanical causes should be considered.

As straightforward as code 36/P1790 may be, having an explanation for it by the manufacturer is tremendously helpful in diagnostics. But when one code sets another without an explanation from the manufacturer as to which code sets first, you may find yourself in that gray area of trial and error that costs time and money. Of course, once you push through that trial-and-error experience and succeed in the repair, the strategy of which code sets another becomes clearer.

One such experience is with a 2003 Acura 3.2TL using a B7WA five-speed automatic transmission. This particular vehicle features both an antilock-brake system (ABS) and a traction-control system (TCS). The basic purpose of ABS is to prevent wheel lock when the driver stands on the brake pedal in panic situations. The TCS steps the ABS up a notch by providing low-speed traction control through the front wheels. While the operator is driving the vehicle (not stepping on the brake), if the TCS detects wheel slippage via the ABS sensors it will apply slight braking force to the slipping wheel to regain traction. Stepping this system up yet another notch is a program called Vehicle Stability Assist (VSA). This system uses additional sensors such as a yaw-rate sensor, which determines the vehicle’s angle. This signal is then compared with those from a steering-angle sensor and vehicle-speed sensor to determine whether the vehicle is in a skid. When it recognizes a skid, the VSA control unit sends a brake signal to the modulator unit, which applies braking force to slow the spinning wheel. It can individually apply the brake to one, two, three or all wheels in an attempt to pull the car out of a skid. As the VSA is controlling wheel spin, it simultaneously sends a traction-control signal to reduce engine power by retarding spark or cutting fuel.

With explanations of these various systems now given, ABS codes are listed as a two-digit code followed by a -1 (primary system); traction-control codes are followed by a -2 (secondary system). For example, ABS code 31-1 would be a right-front inlet solenoid, whereas 31-2 would be a traction-control code for an engine-retard-command (PFINH) signal. I do not know whether PFINH is an acronym, but it refers to the signal sent over a wire as a communication line from the ABS/TCS to the PCM, in this instance to retard the engine.

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The Acura 3.2TL mentioned previously had both a P0740 code for a performance failure of the converter clutch and a TCS code 31-2 PFINH signal. At first one may think they are two separate issues; yet another may think one is affecting the other – particularly since we often have seen various ABS issues affecting transmission operation: late upshifts, no upshifts, loss of high gear, downshift clunks and the list goes on. So the approach has been, in addition to handling all-engine related codes before diagnosing transmission issues, we now have to add all ABS-related complaints beforehand. But as with most things in life, not everything is this black and white. Sometimes engine-related issues have nothing to do with transmission issues, and the same is true with the ABS.

In this particular scenario, the P0740 is what actually caused the 31-2 to occur. There is nothing written by the manufacturers to inform you of this strategy. In fact, we have seen TCS code 36-2 for a TPS output (THLOUT) signal malfunction produce code 31-2. So it appears that if there are any certain types of issues related to engine load, this 31-2 will set, indicating that the TCS is unable to initiate an engine retard while some type of engine-load problem exists. This determination has come by those I have spoken with who through their sweat and tears of spending hours of unpaid time and parts tried to eliminate code 31-2 first. Once the P0740 issue was resolved, 31-2 went away. Apparently the chicken does come before the egg, but in other instances the egg before the chicken. Knowing this may prevent you from having egg on your face, as it did with me.

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