4R100 Input/Output Speed Sensor Symptoms

A 4R100 with a speed sensor problem rarely just throws a code and keeps driving normally. The PCM builds its whole shift plan from speed signals: when to upshift, how much line pressure to command, when to lock the converter. Feed it a bad number and you get a truck that shifts early, late, harsh, drops into neutral, bangs into 1st at a stop, or flashes the O/D OFF light and goes into limp mode. Most of those complaints get blamed on the transmission. A lot of the time the transmission is fine.

This guide covers the three speed inputs a 4R100 truck uses, what each one does, the codes and symptoms that point at each, and how to test them on the truck before anyone buys a sensor or pulls a pan. The resistance specs, part numbers and code definitions come from the ATSG 4R100 manual, ATRA's Ford seminar book and several Transmission Digest case files (full list under Sources).

Recommended 4R100 parts

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4R100 Master Rebuild Kit 1998-2005

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Three speed signals, three jobs

The 4R100 replaced the E4OD starting in the 1999 model year, in F-250 through F-550 Super Duty trucks, E-Series vans and the Expedition, Navigator and Excursion with the 5.4L, 6.8L and 7.3L. Depending on the truck, the PCM can see up to three speed signals.

• Turbine Shaft Speed (TSS). A magnetic pickup that reads the speed of the transmission input. ATSG says it mounts on the top front of the case on some models. The PCM uses TSS to control EPC (line) pressure and converter clutch strategy.
• Output Shaft Speed (OSS). Also a magnetic pickup, mounted on the top of the extension housing. It reads a rotor pressed onto the output shaft. The PCM uses OSS for EPC pressure, shift scheduling and TCC strategy.
• Vehicle Speed (VSS). On these trucks the vehicle speed signal traditionally comes from the rear anti-lock brake sensor in the differential housing, which also drives the speedometer. ATSG's P0500 entry describes it as "vehicle speed input from VSS/ABS."

ATSG is clear that the TSS and OSS are model dependent, so not every 4R100 has both. Look at the case before you start. If there's no sensor on the top front of the case or on the extension housing, the PCM is working from the rear-axle signal and your diagnosis starts at the differential.

Specs and part numbers

Two things to take from that table. First, a non-PTO TSS and the OSS are the same Ford part number, which is handy for a swap test. Second, the PTO trucks use a different TSS with a lower resistance range. PTO was an option only on 8,500 GVW and up Super Duty trucks with the 6.8L or 7.3L. Put a non-PTO sensor in a PTO truck, or measure a PTO sensor against the non-PTO spec, and you'll chase the wrong answer. ATSG gives the sensor bolt torque as 8-10 N-m (71-88 in-lb). It also says to pull both sensors before the unit goes on the bench so they don't get broken during teardown.

Codes and symptoms by sensor

The ATSG code chart for the 4R100 splits the speed sensor codes into three levels of severity:

• P0715 / P0720, insufficient input from TSS / OSS. Sets the code, flashes the TCIL (the O/D OFF lamp) and flashes the MIL.
• P0717 / P0722, TSS / OSS signal intermittent. Sets the code and flashes the TCIL.
• P0718 / P0721, TSS / OSS signal noisy. Sets the code only.
• P0500, insufficient or intermittent vehicle speed input from VSS/ABS. ATSG lists harsh engagements, firm shift feel, an abnormal shift pattern, unexpected downshifts at closed throttle, and a converter clutch that acts up or only applies at wide-open throttle. May flash the TCIL.

Read those symptoms against what each signal controls. A bad TSS mostly shows up as firm shifts (the PCM has lost part of its EPC feedback) and converter clutch complaints. A bad OSS or VSS messes with the shift schedule itself: early or late shifts, hunting, downshifts you didn't ask for. A signal that drops to zero while the truck is moving is the classic sudden-neutral or "stuck in 1st after a stop" complaint. A flashing O/D OFF light on any of these is the PCM telling you it has seen a fault and gone to its failure-mode strategy.

How the PCM decides a speed signal is bad

The "insufficient input" codes are plausibility tests, not resistance tests. Ford's 2004 OBD System Operation Summary describes both checks as continuous monitors with a 30-second duration that only run in a forward range once the PCM has proof the truck is moving: engine speed above converter stall (3,000 rpm), or another shaft sensor showing real speed, or 10 mph road speed. P0715 sets when the truck is inferred to be moving with positive driving torque and TSS stays below 200 rpm for 5 seconds. P0720 sets when OSS stays below 100 to 200 rpm for 5 seconds under the same kind of conditions. That's why a perfectly good sensor reading a part that has stopped turning sets the same code as a dead sensor, and why a quick idle test in Park will never reproduce either code. The full P0715 walkthrough is in our 4R100 P0715 guide.

When you scope a sensor, GEARS Magazine's Sean Boyle recommends checking peak-to-peak AC voltage against a known-good sensor, and he notes that the signal from a magnetic pickup gets weaker at low rpm. A weak reading near idle isn't a failed sensor by itself.

Step 1: Watch the PIDs, not just the codes

Put a scan tool that shows live transmission data on the truck and pull up TSS, OSS, VSS, engine RPM and commanded gear. Record them on a road test if your tool can.

Start key on, engine off, truck parked. Every speed PID should read zero. ATRA's 2003 Ford seminar book has a specific 4R100 bulletin on this: an erratic 1-2 upshift or 2-1 downshift can be caused by a VSS input while the vehicle is stationary. If the scanner shows vehicle speed with the key on and the engine off, the PCM is seeing a phantom signal. ATRA's fix is a Ford jumper kit, part number 1C3Z-13N850-AA, that replaces the PCM's ground wires with a single cable to body ground. The procedure moves the wires in PCM pins 3, 23, 24, 51, 76, 77 and 103 into the kit. That's a grounding problem, and no sensor will fix it.

Then drive it. What you are looking for:

• Dropouts. Any speed PID that dips toward zero and snaps back while road speed is steady. That's a wiring, connector or sensor problem.
• Disagreement. In 3rd, the 4R100 is in direct drive, so TSS and OSS should read the same. In 3rd with the converter clutch applied, TSS should also match engine RPM. If they don't, one of the signals is lying or something inside is slipping.
• A signal that fades with speed. A sensor with too big an air gap may read fine at low speed and get erratic at highway speed, or the reverse.

Step 2: Check the sensor and the circuit

With the connector unplugged, measure sensor resistance and compare it to the table above. Then check each sensor lead to ground. It should be open. A sensor that measures in spec can still be bad, so don't stop there.

These are passive, variable-reluctance sensors. They make their own AC voltage and frequency and need no power feed, which Transmission Digest points out makes them easy to test in the field. With the sensor out of the case, wave a steel screwdriver quickly across the tip and you should see a signal on a meter set to AC volts, or better, on a lab scope. Do this at the PCM end of the harness and you've proven the sensor and the wiring in one shot.

For the rear axle signal, Transmission Digest's write-up on loss of vehicle speed in Ford trucks gives numbers worth keeping on hand. On those trucks, at 30 mph the frequency measured at the RABS sensor test connector was about 667 Hz, and at the PCM input about 67 Hz, because the signal was converted along the way. It also gives the ground rule: voltage drop on the grounds should be no more than 0.3 V, and 0.1 V or less is best. That article covers 1992-and-later trucks with LCD odometers and the E4OD, AODE and 4R70W, so check the wiring diagram for the exact truck before you apply the frequencies to a 4R100. The method and the ground spec carry over.

Its list of causes for a lost vehicle speed signal, most of which live outside the transmission:

• A failed RABS/VSS sensor in the rear differential
• A loose exciter ring on the differential carrier
• Too much silicone on the sensor, which changes the air gap
• A corroded connector or damaged wiring at the sensor
• A failed speedometer/odometer module (PSOM), or lost power or ground to it
• A failed PCM

The same article notes that the PSOM can only be recalibrated a limited number of times: 3 times on 1992 trucks and 6 times on 1993-and-later. Keep that in mind on a truck that has had tire or gear changes. A speedometer that is wrong because of a tire size change also means shift points that are wrong.

Step 3: When the sensor and wiring are good

This is where people waste the most money. Two Transmission Digest case files show why a good sensor doesn't mean a good speed signal.

The rear axle. A 1995 F-250 came in with erratic downshifts and a speedometer that dropped out over 60 mph. No codes. The circuit resistance, wiggle tests and ground checks were all fine. The lab scope showed an erratic, non-symmetric pattern. A new speed sensor didn't fix it and neither did a rebuilt instrument cluster. The problem was in the differential: the tone ring had heavy rust pitting, and so did the ring gear. The limited-slip clutches were worn out, the pinion shaft was badly worn, and the spider gears were galled. After a full rear axle rebuild with a new tone ring, the scope pattern was clean. If a rear-axle signal looks bad on a scope and the sensor is new, pull the cover and look at the tone ring.

The coast clutch drum. A 2004 F-550 with the 6.8L V-10 and a PTO 4R100 came in flashing O/D OFF, shifting erratically, with P0717 set. The first find was an open circuit between the PCM and the TSS, which got an overlay wire. Still no signal. The tech pulled the TSS, hooked a scope to the PCM signal wire and had a helper wave a screwdriver over the sensor tip. Clean waveform, so the sensor and circuit were proven. The key fact: on the 4R100 the turbine speed signal comes from teeth on the coast clutch drum. Looking through the sensor hole with the engine running, the drum spun for a moment after startup and then stopped. The transmission had failed internally, even though it was still going through all four gears.

That second case is the one to remember. A P0715 or P0717 with a proven sensor and circuit is telling you the drum it reads isn't turning the way it should. That's a teardown, not a sensor.

Replacing a 4R100 speed sensor

1. Confirm which sensor with the codes and PIDs, and confirm PTO or non-PTO before ordering a TSS.
2. Clean around the sensor before you pull it so dirt doesn't fall into the case.
3. Look at the tip. Metal fuzz on a magnetic pickup can distort the signal, and it also tells you something inside is shedding metal.
4. Install with a new O-ring, lube it with clean ATF, and torque the bolt to 8-10 N-m (71-88 in-lb). Don't overtighten into the aluminum.
5. Check the connector for corrosion and the harness for rub-through, then clear codes and road test with the PIDs up.

For the rear axle sensor, don't pack silicone around it. The Transmission Digest article lists extra silicone as one of the causes of a changed air gap and a lost signal.

Preventing a repeat

Speed sensor problems keep coming back when the real cause was left in place. Fix grounds to spec. Look at the differential tone ring and gear oil on high-mile trucks with rear-axle complaints. Keep the harness clipped away from exhaust and the frame. And if a TSS code comes back after a new sensor and a good circuit test, move to the inside of the transmission. The 4R100 limp mode guide covers the other inputs that send these trucks into failure mode.

Need parts for this job?

Our 4R100 parts page has scan tools that read Ford transmission and ABS data, solenoid packs, valve bodies and master rebuild kits, with checkout on site. Confirm the model year, engine, PTO or non-PTO, and 2WD or 4WD before you order.

FAQ

What are the symptoms of a bad 4R100 speed sensor?

A flashing O/D OFF light, harsh or firm shifts, early, late or erratic shifts, unexpected downshifts, converter clutch problems, and in the worst case a sudden neutral or a truck stuck in 1st after a stop. A bad TSS tends to show up as firm shifts and TCC complaints, while a bad OSS or rear-axle VSS scrambles the shift schedule and often the speedometer too.

Where are the speed sensors on a 4R100?

Per ATSG, the turbine shaft speed (TSS) sensor mounts on the top front of the case and the output shaft speed (OSS) sensor mounts on top of the extension housing, reading a rotor pressed onto the output shaft. Not every 4R100 has both; they are model dependent. The vehicle speed signal traditionally comes from the rear anti-lock brake sensor in the differential housing.

Are the 4R100 input and output speed sensors the same part?

On non-PTO trucks, yes: ATSG lists Ford F81Z-7M101-AA with a 781-1979 ohm range for both the TSS and the OSS. PTO-equipped trucks use a different TSS, F81Z-7M101-BA, with a 496-1244 ohm range. Check for a PTO cover on the left side of the case before ordering.

Can a 4R100 set P0717 with a good speed sensor?

Yes. In a Transmission Digest case, a 2004 F-550 with a 4R100 set P0717 even though the sensor and wiring were proven good with a scope. The turbine speed signal comes from teeth on the coast clutch drum, and the drum had stopped turning because the transmission had failed internally.

Related guides

• 4R100 P0715: Input Turbine Speed Sensor Causes & Fix
• 4R100 Limp Mode: Causes and Diagnosis
• 4R100 Harsh Shift Causes
• 4R100 Shift Solenoid Symptoms
• 4R100 Won't Shift Into Overdrive
• 4R100 Torque Converter Shudder