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1997 Dodge Grand Caravan Speedometer & Odometer Not Working: P0500 and P0720 Fault Codes Diagnosis

Model: 1997 Dodge Grand Caravan Fault Code: P0500 Posted: 2016-04-10 18:33

My 1997 Dodge Grand Caravan 3.8L V6 with automatic transmission has developed a speedometer and odometer failure. The speedometer and odometer are completely non-functional, though engine performance, tachometer, and other gauges operate normally. I have already replaced both the input and output speed sensors (OSS) in the transmission, but the issue persists. I tested for power to the output sensor (OSS) under three conditions: ignition on, engine running, and transmission in gear. In all cases, no voltage was detected at the sensor terminal. The vehicle displays P0500 (Vehicle Speed Sensor Circuit Fault) and P0720 (AT Output Speed Sensor - Low Output Above 15 MPH) when scanned. I suspect a power supply issue to either the VSS (Vehicle Speed Sensor) or OSS, as both sensors rely on an 8-volt reference from the Transmission Control Module (TCM). The TCM is responsible for supplying this voltage. I have checked all fuses and relays (including PDC fuse #14 and #15), but no power is detected at the TCM output terminals or along the VSS wiring harness. I am seeking guidance on how to verify if the TCM is receiving power, whether there are known wiring diagrams for TCM terminal connections, and what diagnostic steps should be taken before replacing parts. I also want to confirm if this issue could stem from a faulty TCM, damaged sensor wiring, or an internal failure in the speed sensors themselves.

Related fault codes
P0500P0720
Comments (17)
Anonymous 2016-04-11 08:32

Always begin with a full OBD-II scan—even if the check engine light is off—to confirm fault codes and ensure accurate diagnosis.

Anonymous 2016-04-11 08:43

I've scanned the vehicle at three different auto parts stores, and all report a VSS (Vehicle Speed Sensor) fault with identical results.

Anonymous 2016-04-11 08:50

What are the exact diagnostic trouble codes being reported?

Anonymous 2016-04-11 09:19

I’ve just had it scanned again. The speedometer and odometer remain non-functional, and I’ve also performed a key-on-off cycle to trigger diagnostics. All systems appear normal during this test.

Anonymous 2016-04-11 12:46

The error codes are P0720 and P0500.

Anonymous 2016-04-11 16:03

Are these the only codes detected? I suspect this may be a 4-speed transmission (not 3-speed), which is rare but possible. I would expect to see a P0700 code as well. Since both the OSS and ISS are 8V sensors powered by the TCM, I recommend checking whether the TCM is receiving power—verify fuse 14 and 15 in the PDC relay box, and test the output of the TCM relays. A wiring diagram for TCM terminals would be helpful. Reference: http://julien.manche.free.fr/chrysler/a ... ront_1.gif

Anonymous 2016-04-11 22:35

I only tested the OSS so far. I’ll check the ISS tomorrow. Do you mean to verify if power is being supplied by the TCM? I’ve already checked all fuses—how can I test relay output?

Anonymous 2016-04-12 08:07

Don’t just inspect fuses—test continuity on both ends of each fuse. A common troubleshooting step is to swap the suspect relay with a known good one (e.g., horn or fuel pump relay) to isolate the issue. Also, note that some vehicles may not display all codes during a 'key dance' test. Check for voltage at the ISS and OSS—these sensors typically draw power from the TCM. I’m still suspecting a non-responsive TCM and intermittent code detection. Is this issue intermittent? Do you have a remote starter or any other systems that don’t operate properly? *Note: In P176x series vehicles, certain codes like P0750 may be manufacturer-specific and not mil-related.

Anonymous 2016-04-12 11:41

I’ve tested the fuses with a test light—both ends are intact. I recently had it scanned at an auto shop in AZ. The speedometer and odometer remain completely non-functional. Cruise control is also not working. No remote starter. When the rain stops, I’ll check for other symptoms. How can I verify if the TCM is powering up?

Anonymous 2016-04-12 12:54

One way to confirm TCM operation in P176x series vehicles is to test voltage at TCM relay terminals 30 and 87, or at TCM terminals #56, #17, #16. Also check terminal connections at PDC fuse #2 (under hood). Does the horn work? Are there any ABS or SRS warning lights on?

Anonymous 2016-04-12 13:06

No other warning lights are present. The horn functions normally. It’s still raining—may be all day.

Anonymous 2016-04-12 17:41

Vehicle Speed Sensors (VSS) are relatively easy to test using a digital voltmeter (DVOM)—they typically output an AC signal that can be measured while driving. Alternatively, use an OBD-II scanner to monitor sensor output in real time. If the sensors or wiring are not at fault, consider a failing TCM connector or module. A high-end scanner like Launch may help if available locally. Many older Dodge vans have known wiring issues—always test all components before replacing parts. Consider contacting Chrysler directly for an official diagnosis and estimate.

Anonymous 2016-04-13 11:55

No power detected at the OSS or ISS when engine is running. Also, no voltage on the VSS wire at the TCM connected to the PCM. I replaced the relay with a fuel pump relay—no improvement. The wiring between TCM and OSS/ISS appears intact. Where can I find a detailed TCM terminal diagram?

Anonymous 2016-04-13 12:18

Try searching: 'revbase bbb motor wiring diagrams' for accessible schematics.

Anonymous 2016-04-13 13:31

I searched that link—no useful results found.

Anonymous 2016-04-13 15:00

Found this reference: http://www.revbase.com/BBBMotor/Wd/DownloadPdf?id=16537

Anonymous 2016-04-13 15:07

Trouble Code: P0500 (3.8L V6 VIN L Auto) – Vehicle Speed Sensor Circuit Fault Not detecting a VSS signal from the TCM for over 11 seconds. Possible Causes: • Open or grounded circuit in VSS or OSS signal to PCM • Open or grounded power circuit (8V) to VSS or OSS • Open ground circuit for VSS or OSS to PCM • Damaged speedometer pinion or failed VSS sensor P0720 (3.8L V6 VIN L Auto) – A/T Output Speed Sensor - Low Output Above 15 MPH Possible Causes: • Open, shorted to ground, or powered signal (+) circuit in OSS • Open, shorted to ground, or powered signal (-) circuit in OSS • Failed OSS (internal open) • Damaged parking pawl lugs • Failed PCM module