Dtc p0502 - 1999 Oldsmobile Bravada

you can check the transmission fluid if its ok and also the transmission pressure

Don't know where you came up with this Speed sensor A Low Voltage? You googled it ?

P0502 is a stored code that means the powertrain control module (PCM) has detected a low voltage input signal from vehicle speed sensor (VSS) A12345. The designation A typically refers to the primary VSS in systems which utilize multiple vehicle speed sensors1. The code means that the Engine Control Module (ECM) has identified a difference in speed reading between the vehicle speed sensor (VSS) and the wheel speed sensors2. The most common cause of the P0502 trouble code is a faulty vehicle speed sensor4.


That's not what factory service repair manual says about that code ,nothing said about wheel speed sensor.

Circuit Description
The automatic transmission output shaft speed sensor (AT OSS) provides vehicle speed information to the PCM. The AT OSS is a permanent magnet generator mounted to the transmission case. The AT OSS produces an AC voltage as the transmission speed sensor rotor teeth pass through the magnetic field of the sensor. The AC voltage level increases as the speed of the vehicle increases. The PCM converts the AC voltage into a digital signal. The PCM uses the vehicle speed signal to determine shift timing, torque converter clutch (TCC) apply, TCC release, and gear ratio calculations.
When the PCM detects a low output speed and the vehicle has a large engine speed in a drive gear, then DTC P0502 sets. DTC P0502 is a type B DTC.


How to test.

Install a scan tool.
Turn ON the ignition, with the engine OFF.
Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM.
Record the DTC Freeze Frame and Failure Records.
Clear the DTC.
Notice: Support the lower control arms in the normal horizontal position in order to avoid damage to the drive axles. Do not operate the vehicle in gear with the wheels hanging down at full travel.
Raise and support the drive wheels.
Start and idle the engine.
Place the transmission in DRIVE.
Select Transmission OSS on the scan tool.
With the drive wheels rotating, does Transmission OSS increase when the wheel speed increases?

YES or NO

If no do this

Turn OFF the ignition.
Disconnect the PCM connector C1.
Using the J 35616 connector test adapter kit, connect the DMM between PCM terminals C1-64 and C1-65.
Select AC volts on the DMM.
Turn ON the ignition, with the engine OFF.
Rotate the right front drive wheel by hand.
Observe the DMM display.
Can a voltage greater than the specified value be obtained?
0.5 V AC

IF no

Leave the DMM test leads connected.
Measure circuit resistance.
Is the circuit resistance within the specified range?
1,530-1,870 ohms

Is the circuit resistance greater than the specified value?
1,870 ohms


Leave the DMM test leads connected.
Disconnect the AT OSS connector at the transmission.
Is the circuit resistance less than the specified value?
1,530 ohms

Test the high signal circuit (CKT 400) and the low signal circuit (CKT 401) of the AT OSS for being shorted together.
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?


Speedometer
The IPC displays the vehicle speed based on the information from the PCM. The PCM converts the data from the vehicle speed sensor to a 4000 pulses/mile signal. The IPC uses the vehicle speed signal circuit of 4000 pulses/mile from the PCM in order to calculate the vehicle speed. The speedometer defaults to 0 km/h (0 mph) if a malfunction in the vehicle speed signal circuit of 4000 pulses/mile exists or if the BCM sends or receives invalid data with the IPC via serial peripheral interface (SPI).


Has nothing to do with input speed sensor

You have manual trans ?
Manual Transmission - Aisin AR5
Diagnostic Trouble Code (DTC) List/Type
DTC P0502
DTC P0503
DTC P0833
Circuit Description
The vehicle speed sensor (VSS) assembly provides vehicle speed information to the engine control module (ECM). The VSS assembly is a permanent magnet generator. The VSS produces alternating current (AC) as the rotor teeth on the output shaft of the transmission, 2WD, or transfer case, 4WD, pass through the magnetic field of the sensor. The frequency and amplitude of the AC waveform increase as vehicle speed increases.
If the ECM detects no vehicle speed for a specified length of time, while other sensors indicate that the vehicle is moving, DTC P0502 sets. DTC P0502 is a type B DTC.

Diagnostic Aids
Ensure the VSS is correctly torqued to the transmission housing.

Vehicle Speed Sensor Replacement
Removal Procedure
Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle .
Remove the front floor closeout panel. Refer to Floor Panel Tunnel Panel Replacement - Front .
Preliminary Procedures
Raise the vehicle. Refer to Lifting and Jacking the Vehicle .
Remove the exhaust system pipe. Refer to Muffler Replacement
1
Front Tunnel Panel Bolt (Qty: 9)
Notice: Refer to Fastener Notice in the Preface section.
Tighten
9 N·m (80 lb in)
2
Front Tunnel Panel

Your best bet , take it to a qualified repair shop .

Are there any DTC's - diagnostic trouble codes ?in the PCM / BCM ? You have third an fourth below 50 mph but above 50 it down shifts to 2nd gear ,is this what your saying or you don't have 3rd or 4th gears at all ? Which engine did yours come with ? 2.2 L or 4.3 L You trans can set several DTC'S an not all will turn on the check engine light .
DTC B2722 (4.3 L) DTC P0218 (2.2 L) DTC P0218 (4.3 L) DTC P0502 (2.2 L) DTC P0502 (4.3 L) DTC P0503 (2.2 L) DTC P0503 (4.3 L) DTC P0705 (2.2 L) DTC P0706 (4.3 L) DTC P0711 (2.2 L) DTC P0711 (4.3 L) DTC P0712 (2.2 L) DTC P0712 (4.3 L) DTC P0713 (2.2 L) DTC P0713 (4.3 L) DTC P0719 (2.2 L) DTC P0719 (4.3 L) DTC P0724 (2.2 L) DTC P0724 (4.3 L) DTC P0740 (2.2 L) DTC P0740 (4.3 L) DTC P0741 (4.3 L) DTC P0742 (2.2 L) DTC P0742 (4.3 L) DTC P0748 (2.2 L) DTC P0748 (4.3 L) DTC P0751 (2.2 L) DTC P0751 (4.3 L) DTC P0752 (4.3 L) DTC P0753 (2.2 L) DTC P0753 (4.3 L) DTC P0756 (2.2 L) DTC P0756 (4.3 L) DTC P0757 (4.3 L) DTC P0758 (2.2 L) DTC P0758 (4.3 L) DTC P0785 (2.2 L) DTC P0785 (4.3 L) DTC P1810 (2.2 L) DTC P1810 (4.3 L) DTC P1860 (2.2 L) DTC P1860 (4.3 L) DTC P1870 (2.2 L) DTC P1870 (4.3 L) DTC P1875 (4.3 L) .
Shift Pattern This category contains the following topics:
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One forward gear only

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Two forward gears only

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Gear missing or slipping

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No upshift or slipping upshift

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No downshifts

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Non-First gear start

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Refer to First Gear Range Only - No Upshift .

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Refer to Third Gear Only .

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Refer to Second/Third Gear Only or First/Fourth Gears Only .

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Refer to Slips in First Gear .

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Refer to Slipping or Harsh 1-2 Shift .

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Refer to No 2-3 Shift or 2-3 Shift Slips, Rough or Hunting .

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Refer to No 3-4 Shift, Slips or Rough 3-4 Shift .

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Refer to No Part Throttle or Delayed Downshifts .

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Refer to Second Gear Start .

call any auto part store.. I called Auto Zone they read them all off to me...now best of luck YOU got a P1870 ???

Trouble Code: P1870

Transaxle Component Slipping (4T60-E)

Trouble Code Conditions: DTC P0502, P0503, P0740, P0753, P0758, P0785 and P1860 not set, engine started, vehicle driven to a speed of 30-82 at an engine speed of 1000-3000 rpm, Fuel Shutoff inactive, TP angle from 8-35%, commanded gear not in 1st gear and the gear range is D4, TF

P0502 Vehicle Speed Sensor "A" Circuit Low Input

Change the speed sensor or check the wiring to it.

DTC P0502: VSS Circuit Low Input

Circuit Description

The OSS provides vehicle speed information to the PCM. The OSS is a permanent magnet generator mounted to the transaxle case. The OSS produces an AC voltage as the speed sensor rotor teeth pass through the sensor's magnetic field. The AC voltage level increases as the speed of the vehicle increases.

The PCM converts the AC voltage into a digital signal. The PCM uses the vehicle speed signal to determine shift timing, TCC apply, TCC release, and gear ratio calculations. When the PCM detects a low output speed and the vehicle has a large engine speed in a drive gear, then DTC P0502 sets.

Conditions For Running DTC

DTC will run under the following conditions:

• No MAP sensor DTCs P0107 or P0108.
• No TP sensor DTCs P0121, P0122, or P0123.
• No ISS DTCs P0716 or P0717.
• No TFP manual valve position switch DTC P1810.
• The transaxle is in a drive range.
• The throttle angle is greater than 12 percent.
• The input speed is greater than 1500 RPM.
• The engine torque is greater than 50 ft. lbs. (68 N.m).
  

Conditions For Setting DTC

DTC will set under the following condition:

• Output speed is less than 150 RPM for 3 seconds.

Action Taken By PCM

PCM performs the following if DTC is set:

• Illuminates MIL after 2 consecutive trips with a failure signal.
• Freezes shift adapts from being updated.
• Commands maximum line pressure.
• Calculates output speed from input speed, engine speed and commanded gear.
  

DTC P0502 will be stored in PCM history.

The Vehicle Speed Sensor (VSS) may also be referred to as the Output Speed Sensor (OSS).

Your hard start and this code maybe unrelated.

Vehicle Speed Sensor fault

There are three parts of the Vehicle Speed Sensor (VSS) circuit; the VSS, the Powertrain Control Module (PCM) and the wiring between the two. The problem could be in any one, or more, of these parts.
The most likely problem would be with the VSS itself. You can check the VSS signal with a DVOM set to read AC volts. Raise the front wheels off the ground and support the vehicle with jack stands. Never, ever work on a vehicle that is supported by a jack alone. Having a vehicle fall on your chest could ruin your whole day.
Connect the leads of the DVOM to the yellow, C1-64 and purple, C1-65 wires of connector C1 (blue) of the PCM. Be very, very careful you do not damage the connections of the wires. I use a single strand of a multi-strand wire to insert into the connector then connect my leads to that. There is an electrical test kit you can buy but the single strand wire will do quite nicely in a pinch.
Put the key in the ON engine OFF position, place the transmission in DRIVE or NUETRAL and slowly rotate the right front wheel. You should get a reading of 0.4 volts AC. If the reading is good set your DVOM to ohms and measure the resistance of the whole circuit. It should read between 1650 to 3180 ohms. If not you have a problem in the wiring. If both check out good, then the problem is in the PCM.
The PCM will run about $321.45 and about an hour labor to replace and reprogram. The VSS will run about $35.17 and about a half hour to replace. Figure about one hour labor to diagnose the problem. If the problem is in the wiring; that is charged by the actual time it takes to locate and repair the problem.
The VSS is located on the end of the transmission. Remove the right front tire and you will see it. To replace it simply unplug the connector, remove the attaching bolt and remove the VSS from the transmission. Then install the new one, secure the attaching bolt and plug in the connector. Simple as that.


Read more at Suite101: Chevy Impala DTC P0502: 2001 Chevy Impala With A DTC Of P0502 http://autotechrepair.suite101.com/article.cfm/chevy_impala_dtc_p 0502#ixzz0btZFK0Ma
Lone88star


Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/jason_77a19afa8d604dee

you jave a biggie here.
here is some info
CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) monitors the difference between engine speed and transmission output speed. In D3 drive range with the TCC engaged, the engine speed should closely match the transmission output speed. In D4 drive range, with the TCC engaged, the TCC slip speed should be -20 to +60 RPM .

When the PCM detects excessive TCC slip when the TCC should be engaged, then DTC P1870 sets. DTC P1870 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC

• No TP sensor DTCs P0122 or P0123.
• No VSS assembly DTCs P0502 or P0503.
• No TCC solenoid valve DTC P0740.
• No 1-2 SS valve DTC P0753.
• No 2-3 SS valve DTC P0758.
• No 3-2 SS valve assembly DTC P0785.
• No TCC PWM solenoid valve DTC P1860.
• The engine is not in fuel cutoff.
• The engine torque is 40-400 lb ft .
• The TP angle is 12-50% .
• The vehicle speed is 56-112 km/h (35-70 mph ).
• The speed ratio is 0.64-0.95 (the speed ratio is the engine speed divided by the transmission output speed).
• The engine speed is 1500-3500 RPM .
• The gear range is D4.
• The commanded gear is not 1st gear
• The TFT is between 20-130°C (68-266°F) .
• The shift solenoid performance diagnostic counters are zero.