Code 29-Insufficient input veh speed sensor

my$100project

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May 12, 2005
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Just as thread says. Just wondering where to start, and possible problems. a diagram and location of this sensor would probably be helpful as well. Thanks in advance for any help.

Also code 81-Inlet Air Control Circuit malfunction.
a quick note: I do have a multimeter handy and access to a fluke 98 scope.
 
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sunil6784

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How's your idle ? a bad idle is sometimes related to the IAC. Also, just for a test, does your cruise control work ? This is controlled by the vehicle speed sensor too.
 

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
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Code 29 - Vehicle Speed Sensor (VSS) is an electronic sender mounted on the speedo pickup gear on the trans. It works the cruse control for both 5 speed and auto trans cars. The VSS is used to tell the computer to speed up the idle as you slow to a stop. This helps keep the engine from stalling when you slow down for a stop sign or stop light.
Check to see if the electrical connector is plugged into it. Clean the connector & contacts with non flammable brake parts cleaner prior to replacing the sensor, as that may fix the problem. The sensor cost is under $30 and it is easy to replace.

Code 81 – Secondary Air Injection Diverter Solenoid failure AM2. The solenoid valve located on the back side of the passenger side wheel well is not functional. Possible bad wiring, bad connections, missing or defective solenoid valve. Check the solenoid valve for +12 volts at the Red wire and look for the Lt Green/Black wire to switch from +12 volts to 1 volt or less. The computer controls the valve by providing a ground path on the LT Green/Black wire for the solenoid valve.

See http://www.veryuseful.com/mustang/t...ng5.0Vacuum.gif for help on the vacuum line plumbing.
 
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Mrg2783

Member
Apr 1, 2018
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Newport Beach
Code 29 - Vehicle Speed Sensor (VSS) is an electronic sender mounted on the speedo pickup gear on the trans. It works the cruse control for both 5 speed and auto trans cars. The VSS is used to tell the computer to speed up the idle as you slow to a stop. This helps keep the engine from stalling when you slow down for a stop sign or stop light.
Check to see if the electrical connector is plugged into it. Clean the connector & contacts with non flammable brake parts cleaner prior to replacing the sensor, as that may fix the problem. The sensor cost is under $30 and it is easy to replace.

Code 81 – Secondary Air Injection Diverter Solenoid failure AM2. The solenoid valve located on the back side of the passenger side wheel well is not functional. Possible bad wiring, bad connections, missing or defective solenoid valve. Check the solenoid valve for +12 volts at the Red wire and look for the Lt Green/Black wire to switch from +12 volts to 1 volt or less. The computer controls the valve by providing a ground path on the LT Green/Black wire for the solenoid valve.

See http://www.veryuseful.com/mustang/t...ng5.0Vacuum.gif for help on the vacuum line plumbing.
Hey, @jrichker hoping you can help, I'm stumped, I keep getting code 29c. Been this way for months.

I have gone through two new vss sensors that both tested within ohms range, cleaned the harness connector and tested continuity from the harness to pin 3 and pin 6. I have continuity on both wires.

Anything additional you can suggest? Possibly it's the computer at this point?

Thanks
 

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
27,005
2,594
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Dublin GA
Hey, @jrichker hoping you can help, I'm stumped, I keep getting code 29c. Been this way for months.

I have gone through two new vss sensors that both tested within ohms range, cleaned the harness connector and tested continuity from the harness to pin 3 and pin 6. I have continuity on both wires.

Anything additional you can suggest? Possibly it's the computer at this point?

Thanks
More than likely it is the wiring or connector.
Do you have a DVM or Multimeter and know how to use it to measure resistance?
 

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
27,005
2,594
224
73
Dublin GA
Using the diagram below, find the wiring for the VSS sensor.

Measure the resistance of each wire from where it connects to the VSS sensor to the correct pin on the computer.
Check the gray/blk wire (computer pin 3) to the gray/blk wire on the VSS sensor.
Check the pink/orange wire (computer pin 6) to the pink/orange wire on the VSS sensor.
You should see less than 1.5 Ω resistance.

Computer wiring harness connector, wire side
71316.gif


Computer wiring harness connector, computer side
88243.gif



The following are diagrams courtesy of Tmoss & Stang&2birds

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
91-93_5.0_EEC_Wiring_Diagram.gif



See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring; http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.


TFI module wiring for 94-95 Mustang GT
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-IgnitionControlModule.gif

Complete computer, actuator & sensor wiring diagram for 94-95 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/TPS_IAB_Pic.jpg

Starter circuit
http://forums.stangnet.com/attachment.php?attachmentid=21328&d=1080916057

Alternator diagram for 94-95 Mustangs.
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-Alt.gif
 
Last edited:

Mrg2783

Member
Apr 1, 2018
81
3
8
36
Newport Beach
Using the diagram below, find the wiring for the VSS sensor.

Measure the resistance of each wire from where it connects to the VSS sensor to the correct pin on the computer.
Check the gray/blk wire (computer pin 3) to the gray/blk wire on the VSS sensor.
Check the pink/orange wire (computer pin 6) to the pink/orange wire on the VSS sensor.
You should see less than 1.5 Ω resistance.

Computer wiring harness connector, wire side
71316.gif


Computer wiring harness connector, computer side
88243.gif



The following are diagrams courtesy of Tmoss & Stang&2birds

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
91-93_5.0_EEC_Wiring_Diagram.gif



See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring; http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

TFI module wiring for 94-95 Mustang GT
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-IgnitionControlModule.gif

Complete computer, actuator & sensor wiring diagram for 94-95 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/TPS_IAB_Pic.jpg

Starter circuit
http://forums.stangnet.com/attachment.php?attachmentid=21328&d=1080916057

Alternator diagram for 94-95 Mustangs.
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-Alt.gif
Thank you very much! Always appreciated.
 

Mrg2783

Member
Apr 1, 2018
81
3
8
36
Newport Beach
Using the diagram below, find the wiring for the VSS sensor.

Measure the resistance of each wire from where it connects to the VSS sensor to the correct pin on the computer.
Check the gray/blk wire (computer pin 3) to the gray/blk wire on the VSS sensor.
Check the pink/orange wire (computer pin 6) to the pink/orange wire on the VSS sensor.
You should see less than 1.5 Ω resistance.

Computer wiring harness connector, wire side
71316.gif


Computer wiring harness connector, computer side
88243.gif



The following are diagrams courtesy of Tmoss & Stang&2birds

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
91-93_5.0_EEC_Wiring_Diagram.gif



See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring; http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

TFI module wiring for 94-95 Mustang GT
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-IgnitionControlModule.gif

Complete computer, actuator & sensor wiring diagram for 94-95 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/TPS_IAB_Pic.jpg

Starter circuit
http://forums.stangnet.com/attachment.php?attachmentid=21328&d=1080916057

Alternator diagram for 94-95 Mustangs.
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-Alt.gif
Just an update for anyone in the future, I broke down and bought a third VSS and sure enough, it fixed the issue.

I guess the VSS measuring within ohms doesnt mean it is necessarily good.

Third times the charm apparently.

Thanks for the help @jrichker
 
Last edited:

rjohnson92

Member
Jun 23, 2019
5
1
13
26
Florida
Hi I’m having the same issue with my car. I have a 1992 Mustang GT with a fresh build 308 and an A5 transmission. I swapped over the the Dakota digital dash so I know longer have a speedo cable but I have the VSS sensor in place and plugged in. I don’t think I have a gear in the tranny bc again I’m using a Dakota digital dash set up. I’m getting code 29C as well. I will check the resistance in the wires previously mentioned but now that I think about it. If there is no gear in the tranny to spin the VSS sensor, then the sensor isn’t really doing much to tell the computer that the car is moving hence why I stall coming to a stop when pushing In the clutch? My idle is good and it drives good. I still need a tune to make it perfect. Did a base idle reset and set the timing and fuel pressure.

My set as follows:
308 with flat top forged pistons
Fresh built stock bottom end
SVE heads ported and polished
1.6 trick flow rockers
Comp cam hardened push rods
New Ford high performance lifters
Ford E cam
New comp cam timing chain
Edelbrock high flow water pump
Trickflow upper and lower street burner manifold
3.5” Anderson power pipe
30# injectors with the proper calibrated MAF
A5 transmission from astro performance
Dakota digital dash
Live wire wires, NGK plugs, screaming demon coil, MSD distributor
Etc....

Just a little about my ride since I’m new on this site. Thanks in advance for your help. @jrichker

-Ron J.
 
Last edited:

Mustang5L5

Mod Dude
Feb 18, 2001
31,119
7,433
224
Massachusetts
Pull the sensor out and shine a flashlight up the hole. You should easily see a speedo gear centered in the hole about 4-5" in.

Without a functional VSS on mass-air equipped cars, some will report stalling when coming to a stop. Correct the VSS issue and that will go away.,
 

rjohnson92

Member
Jun 23, 2019
5
1
13
26
Florida
I’m almost certain there isn’t. The Dakota digital dash gets the speed through GPS. So the speedo cable is tossed. Would it matter on what size gear to get? Just as long as it spins right??
 

Mustang5L5

Mod Dude
Feb 18, 2001
31,119
7,433
224
Massachusetts
Well, you want it to be somewhat accurate.

What rear gears and tires are you running? They sell speedo kits that are a matched pair and at least get you in the ballpark.

ALWAYS use a new clip to secure the speedo gear. DOn't use a used one. After flexing from an install or two, they like to break causing the speedo gear to walk and then not make contact. Total PITA after you've just installed a trans. SO always use a new clip.

For example, if you have 3.73's...

 

rjohnson92

Member
Jun 23, 2019
5
1
13
26
Florida
Oh ok. The gear will have nothing to do with my speed. I thought that was the gears only purpose besides providing a signal to the VSS? I honestly don’t know the gears in my rear end. I haven’t had to get in there yet.
 

Mustang5L5

Mod Dude
Feb 18, 2001
31,119
7,433
224
Massachusetts
Oh ok. The gear will have nothing to do with my speed. I thought that was the gears only purpose besides providing a signal to the VSS? I honestly don’t know the gears in my rear end. I haven’t had to get in there yet.
It won't have anything to do with your speedometer, but it does tell the ECU your speed so that it will know when you are coming to a stop. I'm sure for that purpose it doesn't need to be 100% accurate, but you don't want to be waaaay off either.

At a minimum, you need the drive gear, and a clip



For the cost, you might as well just buy the entire kit that matches the gear you have in the rear and be somewhat "correct" even if you aren't using it to drive a speedometer
 

rjohnson92

Member
Jun 23, 2019
5
1
13
26
Florida
Don’t I need the other gear that goes in the the tranny and then follow by the VSS? I believe the pictured one is the wrong one??
 

Mustang5L5

Mod Dude
Feb 18, 2001
31,119
7,433
224
Massachusetts
There's two gear in the tranny. One is on the output shaft, and the other one is on the VSS.

Which one are you missing? The one on the VSS?