E4OD Speed Sensor Symptoms: Where the Signal Really Comes From

Search for "E4OD input speed sensor" and you will find a lot of people shopping for a part their truck does not have. The 1989-97 E4OD has no turbine (input) speed sensor and no output shaft speed sensor on the transmission case. Look at the 13-pin case connector and you will find shift solenoids, the coast clutch solenoid, the converter clutch solenoid, the EPC solenoid and the fluid temperature sensor. That is it. The only speed information the computer gets is vehicle speed, and on most E4OD trucks that signal starts at the rear axle, runs through the rear anti-lock brake module and the instrument cluster, and only then reaches the PCM.

That routing is why a bouncing speedometer, a rear ABS light and a transmission that suddenly shifts like it is broken can all be the same fault. Specs and code definitions below come from the ATSG 4R100 manual and ATRA's E4OD/4R100 quick reference, the cluster module details from Ford TSB 96-21-11, and the wiring from HGM Electronics' E4OD speed signal guide. Sources are at the bottom.

Recommended E4OD parts

A speed signal fault is found with a code reader and a scan tool before any part gets replaced: an EEC-IV reader to pull code 452 on 1989-95 trucks, and a Ford scanner that reads the PCM and ABS modules and shows the VSS PID live on 1996-97 trucks. Secure checkout on site.

Ford E4OD OBD1 Scanner EEC-IV Code Reader 1981-1995

$100.99 View part

ANCEL FD500 Ford Lincoln Mercury Full-System OBD2 Scanner - Engine, Transmission, ABS, SRS, 4WD Diagnostics

$140.99 View part

Ford Transmission Scan Tool, All Systems Bidirectional

$187.99 View part

Which speed sensors an E4OD actually has

ATRA's quick reference breaks down every terminal of the E4OD case connector: A not used, B coast clutch solenoid, C TCC solenoid, D shift solenoid 1, E shift solenoid 2, F solenoid power, G and H the fluid temperature sensor, J and K not used, L and M the EPC solenoid. There is no speed sensor circuit in the transmission harness. Anything you are testing for speed lives somewhere else on the truck.

Where it lives depends on the year:

The changeover year varies by body style, so trace the wiring on the truck in front of you. If someone tells you to replace the "input speed sensor" on a true E4OD, they are thinking of a different transmission.

What the 4R100 added

ATSG's 4R100 manual describes the output shaft speed (OSS) sensor as a magnetic pickup "added to the top of extension housing," triggered by a rotor pressed onto the output shaft. To make room, the park gear also became a press fit on the output shaft, and the number 13 thrust washer between the case and park gear became a needle bearing. The turbine shaft speed (TSS) sensor mounts on the top front of the case on some models. The PCM uses OSS for EPC pressure, shift scheduling and converter clutch strategy, and TSS for EPC and converter clutch strategy. None of that hardware exists on a 1989-97 E4OD case.

Ford says the same thing in its own emissions paperwork. The 1996 and 1997 OBD System Operation Summaries title the E4OD section "4R100 (E4OD) (RWD) Transmission (no turbine speed sensor)," and the only speed input listed under it is the vehicle speed sensor. The PCM checks that input for rationality: if engine rpm is above converter stall and load is high, the truck must be moving, and a VSS reading under about 1 to 5 mph for 5 seconds sets P0500. Because there is no turbine sensor, Ford's 1996 strategy judges shift solenoid faults by watching for the rpm drop each commanded shift should cause. That makes the VSS even more important on this unit. Our E4OD P0500 guide walks through that monitor and the live-data diagnosis step by step.

How the 1992-97 speed signal gets to the PCM

On most E4OD trucks built from 1992 on, the speed sensor sits in the top of the rear differential housing, reading a toothed exciter ring bolted to the ring gear. It is a magnetic pickup that generates an AC signal whose frequency rises with road speed. That raw signal goes to the rear anti-lock brake (RABS) module and to the Programmable Speedometer/Odometer Module (PSOM) on the back of the instrument cluster.

The PSOM does the math. It is programmed with the truck's tire size and axle ratio, turns the axle sensor signal into a speedometer reading, and sends a standardized vehicle speed signal on to the PCM and the speed control. Ford's standard for that kind of conditioned signal on this era of vehicle is 8,000 pulses per mile, the same figure Transmission Digest describes [4] for the Ford ABS-derived speed signal on the AX4N. HGM Electronics' E4OD wiring guide identifies the processed speed signal wire as gray/black (GY/BK), found at PSOM terminal 7 or PCM terminal 3.

Every link in that chain can take the transmission down. A fault ahead of the PSOM usually kills the speedometer too. A fault between the PSOM and the PCM can leave a perfectly good speedometer and a transmission that shifts badly, which is the one that fools people.

Symptoms of a lost or bad speed signal

ATSG's code chart lists what the truck does with "insufficient or intermittent vehicle speed input from VSS/ABS":

• Harsh engagements and firm shift feel. Without a trustworthy speed input the computer defaults toward higher EPC pressure.
• Abnormal shift pattern. Shift points are scheduled on vehicle speed and throttle. If the speed reading is wrong, the shift timing is wrong.
• Unexpected downshifts at closed throttle. A signal that drops out for a moment tells the computer the truck just slowed down, so it downshifts, then upshifts when the signal returns. On the road it feels like the truck is hunting between gears for no reason.
• Abnormal converter clutch operation, or the converter clutch engaging only at wide open throttle.
• A flashing overdrive light (TCIL) on the shifter.

Add the rest of the chain: a speedometer that drops out or bounces, cruise control that kicks off, and a rear ABS lamp if the axle sensor or its wiring is at fault.

Needle waver and surge at highway speed

Ford documented one version of this in TSB 96-21-11, which covers 1992-96 Aerostar, Bronco, Econoline and F-150 through F-350. The complaint: the speedometer needle wavers, or a light surge occurs, when speed control is used between 50 and 70 mph. Ford traced it to slight dents or chips in the exciter ring or the sensor, and to the air gap between them. The bulletin specifies an air gap of 0.015-0.020 inch (0.38-0.51 mm) and exciter ring runout of no more than 0.004 inch (0.1 mm), and checks that the ring is mounted properly to the ring gear. The repair was an updated PSOM with more immunity to that signal variability [3].

The codes

1989-95 EEC-IV trucks do not have OBD-II P-codes. Pull the key-on engine-off test, the engine-running test and continuous memory. The vehicle speed sensor input fault on these trucks is service code 452. It is a memory code and will not light the check engine lamp on its own, so a truck can shift erratically for months with nothing on the dash but a flashing overdrive light.

1996-97 OBD-II trucks: the vehicle speed code is P0500, which ATSG defines as insufficient or intermittent vehicle speed input from VSS/ABS. On a 4R100, the transmission speed sensors add their own codes. ATSG's chart lists:

P0715 or P0720 on a truck you thought was an E4OD means check the ID tag: it is a 4R100.

Testing the speed signal chain

1. Does the speedometer work?

This one question splits the diagnosis in half on a 1992-97 truck. A dead or erratic speedometer means the fault is at or ahead of the PSOM: the axle sensor, exciter ring, wiring or the PSOM itself. A steady, accurate speedometer with the transmission still acting up points at the PSOM output or the GY/BK wire to the PCM, or at a fault that is not speed-related at all.

2. Check the signal at the PCM

Backprobe PCM terminal 3 (GY/BK) with the harness connected. On the road, with a scope or a meter that reads frequency, the signal should appear as soon as the truck moves and climb steadily with speed. With a scan tool on a 1996-97 truck, watch the VSS PID and compare it to a GPS speed reading. A dropout that lines up with the bad shift is your answer. No signal at the PCM with a working speedometer means the wire from PSOM terminal 7 to the PCM, or the PSOM output.

3. Test the axle sensor

Unplug the sensor and check resistance across its two terminals and from each terminal to ground. An open coil, a near-zero reading or any continuity to ground condemns it. For reference, ATSG gives the 4R100 OSS as a magnetic pickup reading 781-1979 ohms [1]; use the service manual spec for the axle sensor on your truck. Then spin a rear wheel with the truck safely supported and watch AC voltage or frequency at the sensor. It should produce a clean, rising signal.

4. Inspect the sensor and exciter ring

Pull the sensor from the top of the differential. Metal fuzz stuck to the magnetic tip is common and will smear the signal. Look at the tip for damage from contact with the ring. With the cover off, inspect the exciter ring for chipped or bent teeth and check that it is tight to the ring gear. Ford's TSB numbers apply: 0.015-0.020 inch air gap and no more than 0.004 inch ring runout.

5. Check the wiring along the frame

The axle sensor lead runs along the frame rail, close to the exhaust and exposed to road debris. Look for chafe, melted insulation and green corrosion in the connectors. HGM notes the RABS sensor connection is under the hood near the driver's side hood hinge, which makes a convenient point to test the sensor signal without crawling under the truck.

6. Suspect the PSOM last, but do suspect it

Ford's own bulletin replaced the PSOM for an erratic signal. If the sensor, ring, air gap and wiring check good and the signal leaving the PSOM is missing or erratic, the module is next. A replacement or used cluster must be programmed for the truck's tire size and axle ratio, or the speedometer and shift points will both be off.

Do not forget the rest of the list

Speed signal problems share symptoms with several other E4OD faults. Before you buy parts, rule these out:

• Wrong tire size or axle ratio programming. Bigger tires or a gear swap without reprogramming the PSOM makes the computer think the truck is slower than it is. Shifts come late and the converter clutch timing is off, with no code at all.
• Range sensor connector damage. Transmission Digest's Randy Peterson documented a 1992 Bronco with an E4OD that downshifted, slammed back into gear, and would not upshift. The cause was a manual lever position sensor connector with backed-out pins, damaged insulation and wires in the wrong positions, not a speed sensor.
• Engine inputs. ATSG's chart shows MAF and throttle position faults causing firm shifts and abnormal shift schedules on their own. Fix engine sensor codes first.
• Failsafe. ATRA's quick reference shows what the E4OD does with no solenoid control: Drive gives 4th, 2 gives 2nd, 1 gives 2nd. A truck that starts in 4th and has no upshifts at all is in electrical failsafe, which is a different problem from a bad speed signal.

The fix, in order

1. Identify the unit (E4OD or 4R100) and pull all codes, including continuous memory on EEC-IV trucks.
2. Use the speedometer to split the chain: dead or erratic means sensor, ring, wiring or PSOM; good means the PSOM output or the wire to PCM terminal 3.
3. Test the axle sensor, exciter ring and air gap, and repair frame-rail wiring before replacing the PSOM.
4. Confirm PSOM programming for the real tire size and axle ratio, then clear codes and road test. Shifts should come at consistent speeds with the overdrive light off.

Need parts for this job?

Our E4OD parts page has code readers for the EEC-IV trucks, solenoid packs, valve bodies and rebuild kits sorted by year range, all on our own checkout.

FAQ

Does the E4OD have an input or output speed sensor?

No. The 1989-97 E4OD case connector has no speed sensor circuit at all, per ATRA's terminal chart. The computer gets vehicle speed from a sensor elsewhere on the truck, on most 1992-97 trucks the rear axle sensor through the RABS module and the PSOM. The output and turbine shaft speed sensors arrived with the 4R100 in 1998.

What happens when an E4OD loses the speed signal?

ATSG lists harsh engagements, firm shifts, an abnormal shift pattern, unexpected downshifts at closed throttle, abnormal converter clutch operation and a flashing overdrive light. The speedometer usually quits or bounces too if the fault is at or ahead of the PSOM.

Where is the speed sensor on a 1992-97 Ford truck with an E4OD?

On most of these trucks it sits in the top of the rear differential housing and reads an exciter ring on the ring gear. The same sensor feeds the rear anti-lock brakes and the speedometer, and the PSOM in the cluster passes a processed speed signal to the PCM on the gray/black wire at PCM terminal 3.

What code does a bad speed sensor set on an E4OD?

On 1989-95 EEC-IV trucks it is service code 452, a memory code that does not light the check engine lamp. On 1996-97 OBD-II trucks it is P0500. A 4R100 can also set P0715 for the turbine shaft sensor and P0720 for the output shaft sensor.

Can a bad PSOM cause E4OD shifting problems?

Yes. The PSOM passes the speed signal to the PCM, so a failing PSOM or the wire from it can cause erratic shifts even with a good axle sensor. Ford TSB 96-21-11 replaced the PSOM on 1992-96 trucks for speedometer waver and surge caused by speed signal variability.

Related guides

• E4OD Limp Mode Causes and Fix
• E4OD Harsh Shift Causes and Fix
• E4OD Won't Shift Into Overdrive
• E4OD Pressure Control (EPC) Solenoid Symptoms
• 4R100 vs E4OD: The Differences