Throttle Position Sensor Output Circuit Low
The P2621 code indicates that the Engine Control Module (ECM) has detected a low voltage signal from the throttle position sensor (TPS) output circuit. This typically means the signal voltage is below the expected range (usually below 0.2-0.5 volts at idle). The TPS is a potentiometer that tells the ECM the position of the throttle plate. A low output can be caused by a faulty sensor, wiring issues (short to ground, open circuit), poor connector contact, or a problem with the ECM itself. This code often triggers the check engine light and may affect throttle response and transmission shifting.
1. Most Common Causes
- Faulty throttle position sensor
- Short to ground in TPS signal circuit
- Open circuit in TPS signal wire
- Corroded or damaged TPS connector
- Failed ECM (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Poor acceleration or hesitation
- Reduced engine power (limp mode)
- Rough idle or stalling
- Transmission shifting issues
3. Step-by-Step Diagnosis
Step 1: Connect a scan tool and verify the code P2621. Check freeze frame data for conditions when the code set.
Step 2: Visually inspect the TPS connector and wiring for damage, corrosion, or loose pins. Repair as needed.
Step 3: With key on engine off, backprobe the TPS signal wire and measure voltage. Should be ~0.5V at closed throttle and ~4.5V at wide open throttle. If low, check reference voltage (5V) and ground.
Step 4: If voltage is low and reference/ground are good, disconnect TPS and measure resistance across its terminals. Replace if out of spec.
Step 5: If all checks pass, suspect an ECM issue. Perform a wiggle test and check for intermittent shorts. Replace ECM only as last resort.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. The vehicle may enter limp mode, reducing power and potentially causing unsafe driving conditions. Have it diagnosed promptly.
How much does it cost to fix?▼
Typically $50-$150 for a TPS replacement, including parts and labor. Diagnostic fees may add $50-$100. ECM replacement is more expensive ($300-$800).
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.