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DTC codes / GM codes / P1644

P1644 · GMTP Output Circuit

P1644 on GM vehicles indicates that the powertrain control module (PCM) has detected an abnormal condition in the throttle position (TP) output circuit, which is the signal path from the TP sensor to the PCM or from the PCM to other modules. The PCM monitors the voltage on this circuit and sets the code when the signal is out of expected range, stuck, or intermittent, often affecting throttle response and transmission shift feel.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Hesitation or stumble during acceleration
  • Erratic or delayed transmission shifts
  • Reduced engine power or limp mode in some cases
  • Poor fuel economy or increased emissions
  • In rare cases, the engine may stall or idle poorly

Common causes, most likely first

  1. Faulty throttle position sensor (TP sensor) or its internal contacts
  2. Damaged or corroded wiring in the TP output circuit (open, short, or high resistance)
  3. Loose or contaminated electrical connector at the TP sensor or PCM
  4. Failed PCM driver or internal circuit issue (less common)
  5. Aftermarket accessories or poor previous repairs tapping into the TP circuit
  6. Water intrusion or corrosion in the harness near the throttle body

How to diagnose and fix it

  1. Scan all modules for stored codes and freeze-frame data to confirm P1644 is active and not history
  2. Visually inspect the TP sensor connector and wiring for corrosion, chafing, or loose pins
  3. Backprobe the TP sensor signal wire and compare voltage to the manufacturer's specification through the full throttle range
  4. Check for continuity and resistance on the TP output circuit between the sensor and PCM, looking for opens or shorts
  5. Test the TP sensor with a multimeter for smooth resistance change without dead spots
  6. If wiring and sensor test good, verify PCM operation and consider reflashing or replacement only after all other tests pass
  7. Clear codes and perform a road test to confirm the repair and ensure the code does not return

TP circuit checks before replacing parts

  • A common misdiagnosis is replacing the throttle body or APP sensor when the actual fault is a chafed wire in the harness near the throttle body, so always wiggle-test the harness while watching live data.
  • P1644 can be set by a poor connection at the PCM connector even if the TP sensor itself is perfect, so inspect and clean both ends of the circuit.
  • On some GM vehicles, a weak battery or charging system issue can cause false TP circuit codes, so verify battery voltage and ground integrity first.
  • Aftermarket remote starters or alarm systems that tap into the throttle position signal can introduce noise and set this code intermittently.
  • The code may appear only during certain driving conditions, such as cold starts or high underhood temperatures, so use freeze-frame data to replicate the fault.

Can I keep driving with P1644?

If the check engine light is on but the vehicle drives normally, you can drive to a repair shop, but avoid aggressive acceleration or heavy loads. If the engine hesitates, shifts erratically, or enters limp mode, stop driving and have the vehicle towed to prevent unsafe operation.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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