Sometimes It's Not So Bad When It's Bad - Transmission Digest

Sometimes It’s Not So Bad When It’s Bad

The input-shaft and output-shaft speed sensors used in the AF23/33-5 (AW55-50SN) are two-wire Hall-effect sensors, which means they are supplied with a voltage source on one wire and send a signal back to the computer on the remaining wire.

Sometimes It's Not So Bad When It's Bad

Technically Speaking

Subject: Diagnosing speed-sensor problems
Unit: AF23/33-5 (AW55-50SN)
Essential Reading: Rebuilder, Diagnostician
Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

Technically Speaking

  • Subject: Diagnosing speed-sensor problems
  • Unit: AF23/33-5 (AW55-50SN)
  • Essential Reading: Rebuilder, Diagnostician
  • Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

The input-shaft and output-shaft speed sensors used in the AF23/33-5 (AW55-50SN) are two-wire Hall-effect sensors, which means they are supplied with a voltage source on one wire and send a signal back to the computer on the remaining wire.

GM’s technician guide contains a misleading statement that the sensor is supplied with a reference voltage of 0.6 volt. It also stipulates that the size of output voltage does not depend on a rotation number and is fixed at 1.4 volts. Accompanying these statements is a graph showing a square-wave pulse that starts at 0.6 volt and is driven as high as 1.4 volts.

So without a vehicle, this information was difficult to process to the place where you really felt you knew what it was talking about. We could assume what these statements mean on the basis of the graph, but nothing is better than the real deal: a car and a voltmeter. And that is what we have, a 2003 Saturn Vue in failsafe. The scan tool in figures 1 and 2 reveals that we have an input-speed sensor (ISS) that is down.

What is really nice about diagnosing this sensor is that the ISS and the TCM are right there in front of the engine compartment, and you can see them as soon as you open the hood (see Figure 3). And since the output-speed sensor (OSS) was also easy to get to (see Figure 4), I was able to attach an eight-channel PC-based diagnostic scope from ATS onto all four wires (see Figure 5).

This way I could compare both the voltage-supply and signal wires of the ISS with those of the OSS.

  • Channel 1 is reading the ISS signal wire
  • Channel 2 is reading the ISS power wire
  • Channel 3 is reading the OSS signal wire
  • Channel 4 is reading the OSS power wire

With the “key on engine off,” the meters reveal that both the ISS and the OSS are supplied with near-system voltage. Neither sensor is being excited, yet the ISS is showing 7.4 volts and the OSS is showing 1.6 volts. Since the OSS is working and the ISS is not, this could mean only that either the sensor is bad or that the signal wire is shorted to power somewhere between the sensor and the TCM. So the ISS was unplugged and the signal wire was checked for voltage, and there was none. This eliminated the possibility of a short to power, and I concluded that the ISS was defective.

Once the ISS was changed the readings were nearly the same as those of the OSS (see Figure 6). I then started up the vehicle and the scan tool showed that the ISS was finally producing a speed signal (see Figure 7).

With the ATS E-Scope attached, I switched over to the Stacked Scope display and took the vehicle for a little spin. Figure 8 is a screen capture showing the pulse signals of both the ISS and OSS.

Now, I need to apologize at this point. When I hooked the scope back up to the system, I inadvertently reversed the leads, so the scope will not match what we saw during the meter display in figures 5 and 6. The channels now reflect the following:

  • Channel 1 is reading the ISS power wire
  • Channel 2 is reading the ISS signal wire
  • Channel 3 is reading the OSS power wire
  • Channel 4 is reading the OSS signal wire

I then switched over to the Measure and Deep Record display, where these signals can be looked at more closely. Figure 9 shows an overlap of both the power supply and the pulse signal of the ISS and OSS. At the top of the screen you can see that both sensors are supplied with 12.5 to 13.0 volts when the vehicle is running. The pulse signal of both sensors is visible at the bottom of the screen. Zooming in on these signals, Figure 10 shows that they begin their pulse at 0.6 volt and go as high as 1.6 volts, making for an approximate 1-volt on/off pulsed signal.

Now we can begin to understand a bit more what the GM technician guide was trying to say. Since this is an Aisin-Warner transmission, it wouldn’t surprise me if the information was originally in Japanese and the problem we have is in translation. A better translation would be that the sensor is supplied with system voltage and uses a 0.6-volt reference point and that the amplitude of the output voltage does not depend on a speed signal (or frequency), as it is fixed at 1.0 volt.

Ultimately, though, both the ISS and OSS are quite easy to diagnose with a meter and scope. Replacing the sensor is even easier with the Saturn Vue. So the view is, sometimes it’s not so bad when it’s bad.

Many thanks to Seth at Aaction Transmissions in Miami for providing the Saturn Vue with the ISS problem.

You May Also Like

Trying to Stop the Wheel Hop on Ford Edge with 6F50 Transmission

The 2014 Ford Edge SEL with a 3.5L engine (figure 1) and a 6F50 transmission can also be equipped with an AWD system. This would include a Power Transfer Unit (PTU) attached to the transmission with a rear driveshaft going to the Read Differential Unit (RDU). The RDU comprises a differential assembly along with a

The 2014 Ford Edge SEL with a 3.5L engine (figure 1) and a 6F50 transmission can also be equipped with an AWD system. This would include a Power Transfer Unit (PTU) attached to the transmission with a rear driveshaft going to the Read Differential Unit (RDU). The RDU comprises a differential assembly along with a viscous coupling assembly controlled by an Active Torque Control (ATC) coupling solenoid. The system is designed to monitor vehicle conditions continuously and seamlessly adjust torque distribution between the front and rear wheels. When it is functioning correctly, there should be no perception of this taking place when launching or driving the vehicle. 

Sherlock Holmes Approach to an AB60 No-Move Situation

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult.  Related Articles –

ab60
GM 6T40 Pump Identification Guide

The 6T40 was introduced in 2008 for General Motors front-wheel-drive cars in the Chevrolet Malibu and has gone through several changes throughout its three generations, specifically in the pump area. The 6T40 is closely related to the more lightweight 6T30 and the heavier duty 6T45 and 6T50. Generation one started phasing out during the 2012

Seeing the Forest AND the Trees

They say that the proverbial phrase “I couldn’t see the forest for the trees” means that a person or organization cannot see the big picture because it focuses too much on the details. Related Articles – TASC Force Tips: Hydraulics Fundamentals: Check Valves – Shift Pointers: Mazda Sensitive to Pressure – Transmission Testing & Repairs:

The Manifold Pipeway

The Honda six-speed transmission has been on the bench of many specialty shops for one reason or another (figure 1). But, for those of you who have yet to lay your hands on one, mounted on the upper side of the unit is one of the largest, if not the largest solenoid and pressure switch

Other Posts

The Subaru mystery burn

The Subaru TR580 transmission is known for having torque converter clutch solenoid failures. An example of this can be seen in Figures 1 (above) and 2 (below). Related Articles – The torque converter can of worms: Lockup and aftermarket programming – Shift Pointers: Where’s that fluid leak coming from? – Multitasking: Sorting out multiple issues

Tech-Speak-May-Figure-1-1400
Ford 8F24 mechanical diode failure

Mechanical diode failure in automatic transmissions is not uncommon. As far back as the AODE/4R70 shops have seen this type of failure. In April 2022 an article was published in Transmission Digest called, “The ins and outs of the Hydraulic Selectable One-Way Clutch (SOWC).” This article provided photos of the type of damage this style

Tech-Speak-April-Figure-1-1400
Sometimes, a diagnostic code is all you need

With ATSG having the opportunity to help shops solve problems, sometimes we get faced with some real doozies. A shop will call and give us a laundry list of DTCs, leaving us to think someone must have a bulkhead connector unplugged. We then go through the arduous task of deciding which codes prompted other codes

10L80 and 10R80 pump gear differences

You may have seen an article in the August 2023 issue of Transmission Digest called “GM 10L80: A new kind of pump noise,” which goes over how the front cover housing in the 10L80 is fitted with a converter drive gear and idler gear. The idler gear drives the pump’s driven gear, and is press