Code
P1743
CADILLAC
P — Powertrain
TP Signal From ECM
Views:
UK: 19
EN: 30
RU: 31
AI status
Completed
Completed
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Causes
- Open, shorted, or high-resistance wiring between ECM and TCM
- Corroded, loose, or damaged connectors at ECM or TCM
- Faulty throttle position sensor (TPS) or accelerator pedal position sensor (APP) on the engine side
- Faulty ECM sending incorrect TP data to TCM
- Faulty TCM incorrectly interpreting the TP signal
- Interference from aftermarket electronics or PCM flashing/misprogramming
Symptoms
- Malfunction Indicator Lamp (MIL) or transmission warning light illuminated
- Harsh, delayed, or erratic shifts; upshift/downshift issues
- Transmission may go into limp/limit mode
- Poor throttle response or inconsistent engine idle (if TPS is failing)
- Stored transmission-related diagnostic codes in addition to P1743
What to check
- Read all stored codes and freeze-frame data with a capable scan tool (ECM and TCM)
- Capture live TP, TP2 (if present), 5V reference, and signal ground values from the ECM while exercising the throttle
- Compare TP values reported by ECM and TCM (they should match closely)
- Visually inspect wiring harnesses and connectors at ECM, TCM and inline junctions for damage, corrosion or water intrusion
- Backprobe TP signal, 5V reference and ground at the ECM and at the TCM; check for continuity between modules
- Check for technical service bulletins (TSBs) or calibration updates for ECM/TCM relating to TP communication
Signal parameters
- TP sensor voltage (typical): ~0.2–0.5 V at closed throttle, rising smoothly to ~4.5–4.8 V at wide open (vehicle-specific)
- Reference voltage: stable ~5.0 V (±0.2 V) supplied to TPS/APP
- Signal ground: near 0 V with low resistance to battery negative
- No spikes, dropouts or abrupt steps in TP voltage while slowly rotating throttle
- ECM and TCM TP values should track within a few tenths of a volt and follow the same ramping behavior
Diagnostic algorithm
- Retrieve and record fault codes from both ECM and TCM; note freeze frame data and occurrence conditions
- Clear codes and attempt to re-create the fault while watching live TP data on both ECM and TCM channels
- Visually inspect connectors and harnesses at ECM and TCM; unplug and inspect pins for corrosion, bent pins, or pushed-out terminals
- Backprobe the TP signal, 5V reference and ground at the ECM connector: verify voltage levels and smooth response while slowly opening and closing the throttle
- Backprobe the same circuits at the TCM and verify continuity and that the TCM sees the same TP values as the ECM
- If mismatch exists between modules, check continuity and resistance of the signal and ground wires between ECM and TCM (repair any open/shorts)
- If wiring checks good but signal out of range at ECM, test TPS/APP sensor per manufacturer procedure (voltage sweep, resistance as required) and replace sensor if out of spec
- If ECM is supplying incorrect TP values and TPS tests good, consider ECM reprogramming or replacement (verify latest calibration and flash history)
- After repairs, clear codes, perform a road test and confirm TP values track and code does not return; perform final scan of both ECM and TCM
Likely causes
- Poor connection or corrosion at TP signal or 5V reference circuit connector
- Broken or chafed harness between ECM and transmission control module
- Failed throttle position sensor or dual-sensor mismatch (if equipped)
- ECM software fault or calibration mismatch after replacement or update
- Intermittent ground or reference voltage problem
Fault status
Status
TCM reports a TP (throttle position) input from the ECM that is out of expected range, inconsistent with ECM reports, or intermittent. Code may set MIL and affect shift strategy until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 1.5-3.5 hours
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